HENRY C. STETSON GEOLOGICAL LIBRARY WOODS HOLE, MASSACHUSETTS D m ir □ □ D m a /i. C vf-riT U. ^^i Marine Biological Laboratory Library Voods Hole, Massachusetts Gift of Thomas R. Stetson - 1979 AN INTRODUCTION TO THE STUDY OF FOSSILS •Tl H52?<^° THE MACMILLAN COMPANY NEW YORK • BOSTON • CHICAGO • DALLAS ATLANTA • SAN FRANCISCO MACMILLAN & CO., Limited LONDON • BOMBAY • CALCUTTA MELBOURNE THE MACMILLAN CO. OF CANADA, Ltd. TORONTO wo 7/ AN INTRODUCTION TO THE STUDY^- OF FOSSILS (PLANTS AND ANIMALS) BY HERVEY WOODBURN SHIMER, A.M., Ph.D. ASSOCIATE PROFESSOR OF PALEONTOLOGY IN THE MASSA- CHUSETTS INSTITUTE OF TECHNOLOGY Neto gorfe THE MACMILLAN COMPANY 1921 yl// rig^hts reserved Copyright, 1914, By the MACMILLAN COMPANY. Set up and electrotyped. Published November, 1914= NoriDOOl) ^3«2S J. S. Gushing Co. — Berwick & Smith Co, Norwood, Mass., U.S.A. MY WIFE COMRADE AND COLLABORATOR THIS BOOK IS DEDICATED PREFACE This little volume has grown out of a need experienced by the author during fifteen years of teaching paleontolog}^ He has found that students come to the subject either with very little previous training in biology, or at best with a training which has not been along the lines that would definitely aid them in understanding fossils. Too often fossils are looked upon merely as bits of stone, differing only in form from the rocks in which they are embedded. Hence to awaken interest in them as once living animals and plants, connected by the wonderful chain of evolution with the animals and plants now living, has been the chief aim of the author's lectures and laboratory work upon introductory paleontology which he here presents. To this end certain living forms have first been discussed as types of their phyla or classes with especial reference to those features which will help the student to understand the related fossil forms considered later. The response which these living forms make to their environment is considered, where they live, how their life is maintained and how they perpetuate their kind. The relation of the soft body to the hard skeleton or shell is especially emphasized, since it is largely through this very intimate relationship that our interpretation of extinct life is made possible. The student may thus reconstruct from the hard parts preserved in the rocks the appearance of the once living animal. The discussion has been kept as free as possible from unnecessary technical terms. Beyond this work of showing how past life may be interpreted by the life of the present, and beyond this first comprehensive view of the animal and plant world, such a book as this need vii viii PREFACE not go. For further and more detailed study of the fossils themselves other books furnish ample material. The author is indebted to many persons for aid in the prepa- ration of this volume, and in particular wishes to express his gratitude to the following for criticism of various portions of the manuscript and for the loan of illustrations : R. S. Bassler of the United States National Museum, Louis Hussakof of the American Museum of Natural History, Gary N. Calkins and Amadeus W. Grabau of Columbia University, John M. Clarke and Rudolph Ruedemann of the New York State Geologic Survey, Charles Schuchert and Richard S. Lull of Yale University, Percy E. Raymond and William F. Clapp of the Museum of Comparative Zoology, Harvard University, Francis N. Balch of Boston, Robert T. Jackson and Joseph A. Cushman of the Boston Society of Natural History, Charles H. Warren and R. P. Bigelow of the Massachusetts Institute of Technology, Edward S. Morse of the Peabody Academy of Science, Salem, and S. W. Williston of Chicago University. To G. R. Wieland of Yale University he feels especially in- debted for most valuable suggestions on, and the loan of illus- trations for, the chapter on plants. The original drawings in the book owe much to the scientific knowledge and personal interest which their delineator, Mr. J. Henry Blake of Cam- bridge, has contributed to their execution. CONTENTS JNTRODUCTION : Organic and inorganic matter Plants and animals distinguished . Fossils .....•• Conditions of preservation . Classification of fossils . Process of fossilization . Restoration of fossils Color ....•• Fossil objects due to inorganic agencies Distortion ..... Pseudo-fossils .... Collecting fossils .... Index fossils Migration, etc. .... Naming of organisms . Composition of hard parts PAGE 1 2 3 3 8 9 17 20 20 21 21 22 22 23 24 25 PLANTS : Division I, Thallophyta Sub-division A, Myxomycetas Sub-division B, Schizophyta Sub-division C, Diatomeae . Sub-division D, Algae . Sub-division E, Fungi . 32 33 33 34 35 40 Division II, Bryophyta 42 Division III, Pteridophyta Order a, Filicales . Order b, Equisetales Order c, Lycopodiales . Order d, Sphenophyllales 44 46 48 51 55 IX CONTENTS PLANTS {Continued) : Division IV, Spermatophyta Sub-division A, Gymnospermae Order a, Cycadofilicales Order h, Cycadales Family 1, Cycadeoideae Family 2, Cycadeae Order c, Cordaitales Order d, Ginkgoales Order e, Coniferales Order/5 Gnetales . Sub-division B, Angiospermae Class 1, Monocotyledones Class 2, Dicotyledones . PAGE 55 56 57 60 60 66 67 69 70 75 75 78 79 ANIMALS: Phylum I, Protozoa General survey of phylum Type of phylum, Amceba proteiis Class A, Sarcodina Summary of class . Sub-class 1, Rhizopoda . Summary and classification of sub-class Living and fossil examples Sub-class 2, Actinopoda Summary and classification Class B, Mastigophora . Class C, Sporozoa Class D, Infusoria Phylum II, Porifera General survey of phylum Type of phylum, Grantia ciliata Sub-class A, Calcarea . Sub-class B, Non-Calcarea Fossil examples Phylum III, Ccelenterata General survey of phylum Class A, Hydrozoa ..... Type, oi cldAS, Sertulaiia pH7nila 83 83 84 88 88 88 88 90 93 93 94 95 95 96 96 99 102 102 103 108 108 108 108 CONTENTS XI ANIMALS {Continued) : General survey of class . Order 1, Graptolithida . Type of order, Diplograptus foliaceus General survey of order . Fossil examples Class B, Scyphozoa Class C, Anthozoa Type of class, Astratigia dan(e General survey and classification of class Fossil examples Class D, Ctenophora . PAGE 112 113 113 115 117 121 122 122 128 131 139 Phylum IV, Platyhelminthes 140 Phylum V, Nemathelminthes 140 Phylum VI, Trochelminthes 141 Phylum VII, Annulata Class A, Archi-annelida Class B, Hirudines Class C, Gephyrea Class D, Chaetopoda . Type of class, Nereis uirens Summary of Chaetopoda Fossil examples 141 142 142 142 142 142 146 146 Phylum VIII, Echin General survey and classification Type of phylum, Asterias forbesi Class A, Cystoidea General survey of class . Type of class, Caryocnfius Fossil example Class B, Blastoidea General survey of class . Type of class, Pentremites odermata 148 148 149 154 154 155 156 157 157 157 Xll CONTENTS ANIMALS {Continued) : Class C, Crinoidea General survey of class . Type of class, Pentacrimcs Fossil example Class D, Asteroidea General survey of class . Fossil example Class E, Ophiuroidea . General survey of class Class F, Echinoidea General survey of class . Type of class, Strongylocetitrotus Fossil example Class G, Holothurioidea General survey of class PAGE 159 159 160 162 163 163 163 165 165 165 165 166 171 171 171 Phylum IX, Molluscoidea General survey and classification Class A, Bryozoa .... Type of class, Biigula aviciilana General survey of class . Fossil and living examples Class B, Phoronida Class C, Brachiopoda . Type of class, Te?-ebratiili>ia s General survey of class Fossil and living examples eptentJ'ionalis 173 173 173 173 176 178 181 181 181 187 193 Phylum X, Mollusca General survey and classification . Class A, Amphineura .... Class B, Pelecypoda .... Type of class, Venus tnercenaria General survey of class . Fossil and living examples Class C, Gastropoda .... Type of class, Busycon canaliculatus General survey of class . Fossil and living examples Class D, Scaphopoda .... 206 206 207 208 208 219 223 234 234 241 244 250 CONTENTS Xlll ANIMALS {Continued) : Class E, Cephalopoda ..... Type of class, Nautilus pompilius . General survey and classification . Fossil and living examples Phylum XI, Arthropoda General survey and classification Class A, Crustacea .... Type of class, Cambarus General survey and classification Sub-class 1, Trilobita Type of sub-class, Triarthrus General survey of sub-class Fossil examples Sub-class 2, Phyllopoda Summary Type of sub-class, Apus Fossil examples Sub-class 3, Ostracoda . Summary Fossil and living examples Sub-class 4, Copepoda . Sub-class 5, Cirripedia . Summary Fossil examples Sub-class 6, Malacostraca Summary and classification Fossil and living examples Sub-class 7, Stomatopoda Class B, Onychophora . Class C, Myriopoda Class D, Arachnida General survey and classification Order 1, Xiphosura Summary of order . Fossil and living examples Order 2, Eurypterida Summary of order . Fossil examples Order 3, Limulava . Orders 4-16 .... PAGE 251 251 259 262 274 274 275 275 284 285 285 290 294 299 299 299 301 303 303 303 304 305 305 305 306 306 306 308 308 309 309 309 311 311 312 312 312 313 314 314 AN INTRODUCTION TO THE STUDY OF FOSSILS INTRODUCTION ORGANIC AND INORGANIC MATTER Matter is either organic or inorganic. Organic matter is arranged in the form of a plant or animal body, and is so called because it is made up of various organs such as those for eat- ing, breathing and reproduction. In the lowest organisms the entire body forms but a single organ. When matter is not thus organized, as in air, earth and water, it is called inorganic. Food in the shape of lifeless matter, including many inorganic substances and those organic substances in which all the organs have ceased functioning, is absorbed by functioning organisms, and in some manner, not understood, is transformed by them into living matter, that is, into protoplasm. For protoplasm is the only living matter, and through its activity is built up such supporting and protecting tissues as the cellulose of plants, the bone and shell of animals. Protoplasm, whether plant or animal, has the following properties which distinguish it from hfeless matter, (i) Chemi- cally it always contains proteids or albumins, — complex com- pounds of carbon, hydrogen, oxygen, nitrogen and sulfur. It contains, on the average, of carbon 52 per cent, of hydrogen 7 per cent, of nitrogen 16 per cent, of oxygen 23 per cent and of sulfur 0.5-2.0 per cent. The nucleoproteids, found in the cell nuclei, contain also a small amount of phosphorus. (The B I 2 AN INTRODUCTION TO THE STUDY OF FOSSILS white of an egg is almost pure proteid plus much water.) (2) Physiologically it has the power of waste and repair, of growth and of reproduction. Living organisms waste away by oxidation, a kind of internal combustion, but continually repair this waste by additions between the existing molecules. If this addition is greater than that necessary for repair, growth occurs. (Inorganic substances, on the other hand, such as crystals, grow solely by external addition.) Living bodies likewise detach portions of them- selves, which thus acquire independent existence and develop into the form of the parent. PLANTS AND ANIMALS DISTINGUISHED Plants and animals differ fundamentally in their food ; the former usually feed upon inorganic, and the latter upon organic matter. As a result of this, plants tend to a life of immobility, deriving their food from the soil, water and air about them. They accomplish this through the agency of the sun's rays, which, working through the green coloring matter, — chloro- phyl, combine the unorganized elements into the complex products, — proteids, carbohydrates and fats. Animals, on the other hand, as a result of searching for their food, tend to a life of mobility, deriving their food from plants or other ani- mals ; hence chlorophyl is absent, and as a consequence of its absence starch is not manufactured and thus cellulose is like- wise wanting. (All animals have freedom of movement at some period of their lives, even those sessile when adult, as the sponge, coral and barnacle, can move from place to place in their embryonic life.) These differences between plants and animals are, however, not absolute ; some of the lower forms of each sub-kingdom have properties which in their full develop- ment characterize the opposite sub-kingdom. For example, among plants, fungi live upon organic matter, many algae, as diatoms, spores of cryptogams and the male sexual element of INTRODUCTION 3 most plants have the power of locomotion; the dodder and most bacteria have no chlorophyl. Among animals the pro- tozoon, Euglena, has chlorophyl, while cellulose is present in some Protozoa and is abundant even in the ascidians of the Chordata. FOSSILS Conditions of their preservation. — i. That they soon be em- bedded in some protective material. In order that a plant or an animal may leave a record of its existence, that is, become a fossil, a speedy entombment within some protective material is necessary. If an organism is left exposed after death, it quickly becomes disintegrated either through decay or through the attacks of living animals. In other words it at once becomes food to living animals and plants ranging in size from bacteria and protozoons to beasts and birds of prey. This disintegration is aided likewise by chemical and mechanical agencies so that the dead organism passes rapidly back into its inorganic elements. The undertow of waves is the strongest mechanical agency in the disintegration of marine organic remains, such as corals, shells and bones. The habitat of the animal controls the kind of protective material in which it may become embedded after death. As protective materials may be noted sedimentary deposits due to water or wind, ashes from volcanic explosions, bog waters, resin, ice, and incrustations from mineral solutions. Occasionally the entire animal or plant is encased by the rapid deposition of silica or calcium carbonate. Such incrus- tations may occur through immersion in springs, as in the geyser area of the Yellowstone National Park. Much more common is preservation by means of water which has perco- lated through or over liniestone beds ; upon the evaporation of the water the lime which it has dissolved is again deposited. This is especially apt to occur in caves or at the margins of limestone ledges. Many remains of Pleistocene man and 4 AN INTRODUCTION TO THE STUDY OF FOSSILS beasts occur in caves of western Europe preserved by such a stalagmite covering. During a time of increasing cold, as at the beginning of the late Glacial Period, the bogs within the colder areas became frozen. In these natural refrigerators remains of plants and animals are well preserved. As resin stickily exudes from trees it is apt to hold all small objects that touch it, especially seeds and insects, and these are soon completely inclosed by it. Fossil resin, known as amber, is found in various parts of the world, but is most abundant in the Oligocene beds along the Prussian shores of the Baltic Sea. The water of peat bogs and marshes has antiseptic properties, and because of this organisms immersed in it decay very slowly. Logs long inclosed in such waters have been dug up and utilized in various regions, such as southern New Jersey. Volcanic eruptions are at times accompanied by very much fragmental material, especially ash. This ash, falling thickly, is apt to bear down with it many insects, and if falling into a shallow lake, will bury them with such other organisms as may be there present. Such showers occurred at times during the Miocene at Florissant in Colorado, and to them we doubtless owe much of the marvelous record of insect life there preserved (Fig. 137)- Similarly, when prevailing winds blow from a dry into a moist region, or from an area without vegetation to one with it, dust will accumulate in the latter region, resulting in time in thick deposits of unconsolidated, fine, porous, siliceous silt. Such deposits, called loess, are especially abundant in North America, Europe and Asia, from Pleistocene times to the present, and are apt to contain land shells. Some loess is of aqueous origin. The coarser wdnd deposits, such as sand dunes, are not likely to contain fossils ; such an unfossiliferous dune deposit is seen in the coarse-grained, white sandstone of Jurassic age in southern Utah. The vast majority of organic remains preserved as fossils INTRODUCTION have been covered with sediment brought by water. Deposits upon the surface of the continent — lake, flood plain, alluvial- fan and playa deposits — are in the zone where erosion is domi- nant and are hence apt to be quickly, geologically speaking, worn awav with all their included organic remains. Those Fig. I. — Diagram to illustrate that the habitat of a plant or animal determines its chance of preservation as a fossil. deposits are thicker and stand a much better chance of preser- vation, which are poured by continent-draining rivers into the sea as a delta and are spread upon its margin as a flood plain (Fig. i). The delta and flood plain of the Ganges and Indus rivers (Early Tertiary to present) and that forming the Mauch Chunk shales (Mississippian) of Pennsylvania are good examples. The seaw^ard portion of these deposits, being more continuously under water, is best able to preserve the organic remains de- posited in it ; hence we find the Greenbrier formation, inter- fingering the Mauch Chunk shales in southwestern Pennsylvania, full of marine fossils. The landward portion is covered with water and its accompanying layer of sediment only during times of flood when the river overflows its banks ; during the rest of the year the level of the ground water sinks to a greater and greater depth, gradually dissolving all soluble objects as it moves, while the air circulates freely through the upper water- free deposits, completing the oxidation of all organic remains there present. The decay of plants or animals is an oxidizing 6 AN INTRODUCTION TO THE STUDY OF FOSSILS process due largely to the multiplication of bacteria. Hence in these more landward deposits an organism encounters many agencies of destruction, both chemical and organic, and stands little chance of preservation (Fig. i). Thus in the Mauch Chunk shales of Pennsylvania and in the Newark beds (an Upper Triassic alluvial fan and flood plain deposit) of Connecti- cut, New Jersey, etc., few fossils occur and these are principally footprints and plant impressions. In portions of the Wasatch and Bridger formations (Eocene flood plain deposits) of Utah and Wyoming more fossils occur, but they are much more abundant in the Florissant beds (a Miocene lake deposit) of Colorado. In short, the more completely air and circulating water are kept away from organic remains the better the chance for their preservation as fossils ; and, accordingly, marine, lake or marsh deposits are more favorable than those of a flood plain, alluvial- fan or playa, while clay or limestone are better mediums than sandstones or coarse ash deposits. It is thus seen that the chances for the preservation of animals or plants varies with their habitat (Fig. i). Inhabitants of mountainous regions where erosion is greater than deposition stand very poor chance for preservation in the fossil state ; those living on low plains and in fresh water are more likely to be preserved ; but it is the marine forms, especially those living upon the sea- floor beyond the breakers but in water still comparatively shal- low, that stand the best chance for preservation (Fig. i). Here at their death the organic forms are quickly covered by the sedi- ment which, brought in by the rivers or torn by the waves from the land, is widely distributed by the drift of the waters. Hence of all organic forms, marine invertebrates stand the best chance of preservation, for they are the most numerous of all animals and they occupy those areas w^here oxidation is slow and where a prolonged sedimentation is apt to occur ; these forms are, accordingly, the most important of all fossils for the cor- relatiofi of strata. It is not strange, therefore, that many species of fossil insects are known each from but a single speci- INTRODUCTION 7 men, and that such a land form as Archaeopteryx — the earliest known bird — is represented by only two specimens and a separate feather, all from the lithographic limestone quarries (Upper Jurassic) of Solenhofen, Bavaria. Species of fossil marine shells, on the other hand, are known by thousands of individuals. 2. That hard parts be present in the organism. To insure preservation it is usually necessary that the organ- ism have some protective structure, such as the shell of a clam, the bones of a reptile, or the woody fiber of a tree, which upon the death of the animal or plant resists decay for a much longer time than do the softer portions. Usually the less fibrous plants and the softer parts of animals — epithelium, nerves, muscles, and even cartilage and horn — quickly suffer decay ; and only the skeleton or the external covering, composed of chitin, silica, or of the carbonate or phosphate of calcium, are preservable. Thus multitudes of animals, such as most proto- zoons, jelly-fish, sea anemones, many bryozoa and mollusks, most worms, the tunicates, most parasites, and the embryos of most animals, which lack such hard parts, are exceedingly rare or entirely wanting as fossils. Since the vast majority of the invertebrates living in the sea or fresh water are naked or provided with very fragile hard parts, it is only the bottom-living forms, which, in their heavy, protective hard parts, are usually preserved. Notwithstanding the rapid decay of all soft tissues they are occasionally preserved, as for example, by freezing in the bog-ice of Siberia, by carbonization (page 13), or even by the taking up of lime phosphate on the part of the epidermal and muscular tissues. Animals without hard parts at times also leave a record of themselves, such as trails (like those due to the tentacles of a jelly-fish), as internal molds (as the sand- fillings of the lobed pouches of the jelly-fish, Fig. 45), or as impressions of the entire jelly-fish, of leaves, etc. Only rarely are plants protected by calcium carbonate or silica (page 26); usually their preservation is due to direct 8 AN INTRODUCTION TO THE STUDY OF FOSSILS replacement, to the formation of external molds or to the pro- cess of carbonization (page 13). Classification of Fossils. — A fossil is the remains oj a plant or animal, or the record of its presence, preserved in the rocks of the earth. The word is derived from the Latin fodere, to dig, and hence has associated with it the thought of something dug up, for in most cases the preservation of a form depends upon its burial. Many geologists restrict the term fossil so as to include evidences of life to the close of the Pleistocene only. According to this definition all post-Pleistocene remains are spoken of as recent, not fossil. Fossilization is the sum of the phenomena by which the re- mains of animals or plants, or the evidences of their presence are preserved in the earth's strata. Fossils may be divided according to the above definition into, I. Fossilized remains of organisms. II. Objects indicating the former presence of organisms. Sometimes these fossils preserve their original composition as when first buried, that is, they are unaltered. At other times they become more or less completely altered by infiltration of minerals from the surrounding rocks, or the more volatile parts are gradually given off, leaving a residue composed very largely of carbon. It is to such fossils only that the term petrifaction, i.e. " turned to stone," should be applied. I. Fossilized Remains of Organisms A. Unaltered (i.e. original). 1. Originally soft portions of the animal preserved. Ex- amples : insects in amber ; mammoths in frozen earth of Siberia. 2. Only hard parts preserved. Examples: many Ceno- zoic shells, bones, teeth, horns. B. Altered {i.e. petrifications) ; these are divided into four main divisions according to the material petrifying them. Al- INTRODUCTION 9 though silica, lime carbonate, and iron pyrites are the most common replacing minerals, 30 to 40 others replace more rarely. 1. Through silicification. — Varying from the merely partial filling of cavities in fossils (even if composed of silica) to entire replacement with silica. Examples : Shells, plants. 2. Through calcification. — Varying from the merely partial fill- ing of cavities in fossils (even if composed of calcium carbonate) to entire replacement with calcium carbonate. Examples : Most fossil corals, brachiopods, echinoderms, mollusks. 3. Through pyritization. — Varying from the merely partial filling of cavities to entire replacement with pyrite or mar- casite. Examples : Shells, Crustacea, plants. 4. Through carbonization. — Animal or vegetable tissue de- composed under water, resulting in a giving off of comparatively more hydrogen and oxygen than carbon, with a resultant con- centration of carbon. Examples : Fish, graptolites, plants. II. Objects Indicating the Former Presence of Organisms A. Molds, external and internal. 1. Imprints of shells, feathers, tree trunks, entire animal (as dog), etc. 2. Tracks of amphibians, reptiles, birds, etc. 3. Trails of worms, crustaceans, etc. 4. Burrows of worms, echinoids, mammals, etc. B. Coprolites. C. Artificial structures. Examples : Birds' nests, early human implements. Fossils unaltered (original) . ^ All organic remains last longer in a region of almost continuous dry or cold than in one which is moister and warmer. In very cold, or very dry, regions, even the softer portions may remain- unchanged for a long time, pre- serving to future ages the entire animal. Thus, examples of the ancient elephant — the mammoth — entombed in the ice and frozen earth of Siberia since the Pleistocene, are so well lO AN INTRODUCTION TO THE STUDY OF FOSSILS preserved that dogs and wolves will eat their flesh. Likewise, remains of the cliff dwellers in Arizona and New Mexico, such as clothing, food, and human bodies, have been preserved in the dry air of that plateau region for at least many hundreds of years. Many Tertiary insects have been preserved in their entirety, except for complete desiccation, without a trace of mineral infiltration, inclosed in amber ; upon this ancient gum as it was exuding from the pine trees, insects settled, and being held fast by the sticky substance, were finally entirely inclosed. Such trees and their gum wxre buried in the sediment beneath the waters of seas or large lakes, thus preserving these ancient insects in all their perfection of form and brilliant coloring. Usually, however, only the hard parts of organisms are pre- served, and but few of these are found in an unaltered state in pre-Cretaceous rocks ; it is principally in the Cenozoic rocks that they thus occur. The unaltered bone is more or less spongy in appearance, something like volcanic pumice or slag, but most of the cavities are canals, continuous and anastomos- ing ; they do not end blindly as do those in slag. These Haver- sian canals, filled during the life of the animal with arteries, veins and nerves, are much larger and more numerous in the interior of the bone than in the more compact and consequently harder outer portion. Non-petrified shells of Cenozoic or older age, besides having lost much or all of their original color, are usually also somewhat chalky in appearance. This chalkiness is due to the loss of the fleshy material which penetrates the living shell, not only vertically, but also horizontally. The abundance of this spongy animal matter may be demonstrated by an experiment. If a recent shell be placed in a dilute acid which is changed frequently, in two or three days the calcium carbonate will be dissolved away but the shape of the shell will still be retained by the animal matter which formerly penetrated it. Thus shells from the Sankaty beds (Pleistocene) of Nan- tucket, Massachusetts, differ from the recent shells only in their porosity and in having lost much of their color. INTRODUCTION II Fossils altered (petrifactions). — Whenever organic remains are inclosed in sediment to which the air has free access, their disintegration is rapid and complete (page 5) ; but if the deposits become very thick before they are raised from the water, free air will be largely excluded and destruction of the fossils will be principally due to the percolation of the water through the strata from higher to lower levels. That heat is not necessary in the solution of shells is seen in many deposits of glacial age. For example, the drumlins in and to the south of Boston Harbor, which have remained sur- face deposits from the time of their formation, contain no shells in the upper half, but below that level they are quite fossil- iferous. Here it could only be the carbonic acid gas, caught by the rain drops while falling through the air, that caused the gradual solution of the shells. Silicification. — If the percolating water is a supersaturated solution of some mineral substance, such as silica or lime, the first step in the petrifaction of the fossil will be the filling of all existing cavities with this substance. In such a case the origi- nal chemical composition of the shell, bone or wood will remain, but with the many minute openings filled with the foreign min- eral. This is the condition of many of the dinosaur and other vertebrate bones of the Mesozoic. Often, however, the petri- faction, or making into stone, is a process of solution and de- position taking place pari passu, and due to the waters being under-saturated with the chemical substances of which the fos- sil is composed, but oversaturated with some other substance. Such a replacement is at times very perfect. The probable pro- cess is that as a molecule of the original structure is removed, a molecule of the depositing substance takes its place ; in this case the finer structure, such as the fiber in wood, or the pores and lamellae in shells, is perfectly preserved. Such preservation of the finer details of structure is seen in many of the sections of the trunks of petrified trees from the fossil forests of the Yellowstone National Park (Fig. 24), from Arizona and from AN INTRODUCTION TO THE STUDY OF FOSSILS many other states. In the case of plants, the wood may act as a sponge, capillary attraction drawing up the siliceous water, while possibly the high density of this liquid would aid the solution and extrusion of the cellulose (woody fiber). This molecular replace- ment is most common with silica, lime and iron. In iron, replacement takes place in the presence of organic substances ; per- colating waters rich in iron and sulfur will be precipi- tated upon coming into contact with these, caus- ing the formation of mar- casite or of iron pyrites (FeS2) (Fig. 2). Silica is soluble in w^aters containing carbon- ates of the alkalis (Na, K) or alkaline earths (Ca, Mg), such as the ordinary water leaching through the soil. This solution (alkaline solvent of silica), coming in contact with the carbon dioxid of a decaying organism, is neutralized and the silica thrown down ; or this precipitation of silica may occur through the agency of the carbon dioxid evolved by a living organism, such as the diatom, which thus manufactures its siliceous skele- ton. The siliceous skeleton of organisms is composed of hydrous silica and is subject to dehydration into chalcedony, or to a later crystallization into quartz. Hence deposits of the minute diatom skeletons (about 40 million to the cubic inch), known as tripolite, are rarely older than the Tertiary, since the older deposits have probably been dissolved and redeposited as chert. Similar replacement by silica occurs very frequently at the surface of a rock ; probably the majority of silicified shells are thus formed. Fig. 2. — Iron replacing lime in the Devonian coral, HcUophyllum halli E & H, from New York. Natural size. The iron forms the ramifying white lines upon each side ; this largely follows the septa, but it branches from these in all directions. INTRODUCTION 13 It is thus seen that the present composition of a fossil is no indication of its original composition, for there may be iron or siliceous replacements (pseudomorphs) of calcareous shells, iron pseudomorphs after chitinous skeletons and plants, and even, as in some sponges, calcareous pseudomorphs after sili- ceous skeletons. The determination of the original composi- tion depends, in such cases, upon comparison of the form of the organism with the nearest living representatives. Carbonization. — If leaves fall into water, they sooner or later sink to the bottom, where they may be noted along the tree-lined margin of any lake or quiet stream ; here compara- tively little free oxygen can reach them. Decay accordingly is very slow and usually but partial, leaving a residue of carbon ; this, made fine by the motion of the water, gives the black color so characteristic of such bottoms. The form of the leaves under these conditions is, accordingly, not preserved, but their presence is indicated by the black color still persisting after these ancient lake and river margins have hardened into rock. Other leaves, though suffering a similar concentration of carbon, fall in a sit- uation that insures their more rapid burial by the mud brought in by the rivers ; they are accordingly preserved as carbonized films, showing all their original veining. This same process would occur in the case of any other form of vegetation or even of animals (Hydrozoa, Crustacea, fish, etc.), if they were buried beyond the reach of those that prey upon them. The process of carbonization is essentially the giving off of marsh gas (CH4), water (H2O) and carbon dioxid (CO2) ; the last cannot be developed to the exhaustion of the carbon, since, compared with air, little free oxygen exists in standing water. Thus wood (6 CeHioOs) under such conditions would eventually yield an anthracite coal (C24H8O). Good examples of carbonized plant fossils occur in the roof shales of coal mines. Remains of animals similarly preserved are likewise abundant ; well-known examples are Hydrozoa (graptolites) in the Utica shales (Ordovician) of eastern New 14 AN INTRODUCTION TO THE STUDY OF FOSSILS York, and fish in the Newark beds (upper Triassic) of New Jersey and Massachusetts. Objects indicating the former presence of organisms. — Molds. — When a leaf falls upon soft mud, it will impress there its form and surface markings ; but the sun may quickly Fig. 3. — Diagram to explain molds, external and internal, and casts. The shell is the common ark, Area transversa from Long Island Sound. A, external surface of right valve ; B, the concave external mold of same valve ; C, interior view of right valve ; D, internal mold of same valve ; E, section through entire shell from hinge-line {h) forward, the shell being embedded in and filled with sediment (w) ; F, external ornamentation impressed upon the internal orna- mentation through the settling of the sediment after the chemical removal of the shell (as from Fig. E) by water percolating through the strata, ext. m., external mold ; h., hinge-line ; int. m., internal mold ; m., matrix, or sediment ; miis., muscle scars; r. v., right valve; sh., shell (or, if shell is removed and this cavity is filled by some foreign substance, this substance is termed a cast of the valve, since it is formed between molds). (X^.) curl its edges so that it will be blown away by the wind. If this impression or mold be covered by sediment, the imprint is preserved without the leaf itself being inclosed. The mold is thus shaped into the form and surface character of the original. If a shell, such as a clam or snail, be covered with sediment, it will impress its external ornamentation upon the surrounding material (Fig. 3, B). The motion of the water aided later by the weight INTRODUCTION 1 5 of the overlying sediment will usually completely fill the interior of the shell, and upon this filling is impressed the shell's internal ornamentation (Fig. 3, D). The external and internal molds have thus the exact form and surface characters of the exterior and interior of the shell. (Good examples of these molds may easily be made by taking a complete clam or ark shell, first dipping it in water, and then filling and surrounding it with plaster of paris moistened to a plastic state.) If the waters percolating through the earth's strata be rich in some solvent, as carbonic acid, and poor in lime, they will dissolve the calcareous shells from between their external and internal molds, and carry them away as a solution of bicar- bonate of lim.e, leaving hollows where were the shells. In such a case one of three things happens : (i) there remains an open cavitv, as in much of the Devonian (Oriskany) sandstone of eastern New York, Pennsylvania and New Jersey ; (2) through the settling of the strata the external mold comes into contact with the internal (Fig. 3, F), and the external ornamentation thus becomes impressed upon the interior markings, as in many brachiopod and pelecypod shells from the Paleozoic ; or (3) a petrifaction will be formed ; i.e. through a change in the direc- tion of flow due to a differential upheaval of the region, or some other cause, the percolating waters become supersaturated with, for example, silica, lime or iron ; these hollows will then be filled and the foreign mineral will be shaped by the molds already formed into a cast (Fig. 3, E). Such a cast will bear an exact surface likeness to the original shell, but will lack entirely its internal structure. It is in such formation of a cast that the external and internal molds perform the true function of molds as usually defined, since they are thus '' that in which something is molded or formed." (Casts of iron fossils must usually be covered with a thin coating of melted paraffin to prevent a rapid rusting (oxidation and hydration) upon exposure to the air.) When the shell has been removed, leaving an open cavity, the shape and ornamentation of the original shell may be ob- 1 6 AN INTRODUCTION TO THE STUDY OF FOSSILS tained by pressing into it dental wax softened by heating in hot water, forming thus an artificial cast. Soft plaster of paris may likewise be used. If, however, the cavity is partially closed, the mold must be destroyed in extracting the cast. This method of restoring the form of the organism must frequently be used, since plants and animals are often coated with stone while the organic structure is still perfectly retained. Upon the decay of the inclosed organism, which occurs rather quickly, there is left a perfect external mold. In the ancient ash-covered town of Pompeii the use of plaster of paris has enabled the workmen to preserve the external form of several men and dogs buried by the fragmental material which fell during the Mt. Vesuvius eruption of 79 a.d. Tracks. — When birds or other animals searching for food walk over the mud fiats of a river or sea, impressions of their feet are left, which when covered with sediment may be pre- served as fossils. Examples of such are the reptile tracks in the Upper Triassic shaly sandstones of the Connecticut Valley (Fig. 153) and the tracks of the Mississippian amphibian, Sauropus primcBVus, in the Mauch Chunk red shales of Penn- sylvania. . Trails. — Similar to the preservation of tracks is that of trails, though many of these are made on the soft sediment beneath the surface of the water. Trails are the irregular mark- ings of animals, such as those due to the crawling of a worm or snail, the dragging tentacles of a jelly-fish, the impressions of the fins of fish or the markings left by the movements of crus- taceans or sea urchins. Burrows. — When a worm burrows and eats its way through rather compact earth the hole remains for some time and finer material may later be washed into it ; when it burrows its way through very moist sediment, as at the seashore, the finer mate- rial is usually carried into the cavity immediately behind it by the water oozing in from the sides. In both of these cases the resultant is a tube of finer material surrounded by coarser ; as, INTRODUCTION 1 7 for example, Scolithus from the upper Cambrian sandstones of the Appalachian region. Burrows are likewise formed in rocks on exposed coasts by sea urchins, in rocks and wood by different species of pelecypods (Lithodomus, Teredo, etc.), in soft earth by mammals. All of these burrows are capable of preservation as fossils under favorable conditions. Coprolites. — The contents of the intestine and the excre- ment of many ancient animals, especially of fish and reptiles, are often preserved and such fossils have received the name of coprolites. These are usually nodular or contorted in appear- ance and phosphatic in composition. They often contain such indigestible remnants of the animal's food as portions of scales, bones, teeth or shells. Recent deposits are known as guano and are largely due to the excrement of sea birds and of such marine mammals as seals. Restoration of fossils. — Since fossil organisms are built on the same general plan as living ones, a reconstruction of their appearance when living, like their identification and classifica- tion, is a matter of comparison. The broader and deeper one's knowledge of living species, the nearer the truth is apt to be one's conclusions. The relation between the soft, unpreservable portions of an animal, and the hard parts capable of preserva- tion, is very close. The shell, for example, is such an intimate part of the animal that an injury to it means a lessening of the vitality of the entire organism, while the loss of it means death (Fig. 4). It is, accordingly, incorrect to speak of the animal and its shell as though the shell were a house which the animal could leave at will. An invertebrate animal may thus be divided, for convenience of description, into body (the soft parts) and shell ; a vertebrate may be considered as flesh and skeleton. In the restoration of a fossil the better preserved the material, the truer to life will be the result. In very fine-grained shales and limestones impressions of the soft parts are often preserved to even minute details. Thus in making a restoration of the trilobite, Triarthrus, extinct since the end of the Paleozoic, the c 1 8 AN INTRODUCTION TO THE STUDY OF FOSSILS Utica shale in New York State furnished not only the legs, anten- nae and gills, but traces of the digestive tube as well (Fig. 126). The Lithographic limestone in Bavaria and the Oxford clays in England show by the preservation of arms, outline of body and A B Fig. 4. — The intimate relationship which exists between the hard shell and the soft body of an animal is seen here in the scallop, Pectcn gibhus borcalis, from the New England coast. A, outer surface of left or upper valve ; B, right valve, with the left showing slightly at the base. The mantle secreting the right valve (B) received an injury when the edge of the shell was the growth line a-a' ; this injury lowered at once the vitality of the entire body, so that anterior growth of both mantles wholly ceased for a time, a fact recorded in the conspicuous growth hne a-a' . Though the animal lived for some time after this injury it never regained its former vitality, as is shown in the development of such old age characters as the obsolescence of the ribs and the irregularity of the growth lines. The mantle at {a) upon the right valve ceased growing entirely but the opening thus made was partially filled by the inbending of the opposite valve. (Slightly reduced.) ink sac that the Mesozoic belemnoids were very similar to the living squid, while in the shale of the Stephen formation of Alberta, occur beautiful impressions of such soft-bodied animals as jelly-fish, worms and sea cucumbers. In trilobites there is usually preserved only the hard dorsal shield ; in belemnoids only the small, internal skeleton ; in worms, teeth ; and in sea cucumbers scattered calcareous plates. In all vertebrate animals muscles are fastened to an internal skeleton by projections, roughened surfaces or depressions upon the latter; the larger such surface or projection, the larger the muscle attached to it. Hence from the bone alone the number and size of the muscles formerly attached to it can be estimated. INTRODUCTION 19 Since muscles and bones make up the main bulk of the animal, a restoration to living proportions is possible. The shape of the teeth tell the character of its diet, which in turn reveals the size of the digestive or- gans. The superficial cover- ing, however, is often a matter of conjecture. In fish the covering of scales is usually preserved; in amphi- bia mucous gland impressions often show upon the surface of the bones, thus indicating a soft, slimy skin for the animal ; in reptiles the pres- ervation of scales or bony denticles or their impressions indicate the character of the external covering (Fig. 5). When, however, as often happens, nothing of the sort is preserved, the restoration must be based upon comparison with fossil and living forms ; especially suggestive are the young of nearly related living species. Studies in evolution have show^n that each individual in its development from the egg to maturity passes through stages which are similar in general to its successive adult ancestors from earliest geologic ages to the present. Hence a stage in the youth of a living animal would be suggestive of related extinct forms. This principle, however, must be applied with the greatest caution. The adult elephant and rhinoceros are almost hairless, while the young have much hair ; that this may be reminiscent of the ancestral forms is suggested by the Pleistocene hairy mammoths preserved in the Siberian ice fields. The coloration of the young likewise is difficult of explanation unless it be taken as representing the Fig. 5. — Natural mold of the surface markings of the dinosaur, Stephano- saurus marginatiis Lambe, from the Cretaceous of Alberta. These mark- ings are from the side of the body, where the yielding mud receiving the impression of the skin of the reptile upon its burial, has preserved them intact though the skin itself has long since disappeared. (From Lambe.) 20 AN INTRODUCTION TO THE STUDY OF FOSSILS coloration of its adult forbears. The young Malayan tapir is longitudinally banded, the adult loses these bands ; the young wild swine are longitudinally banded, the adult are not; the young lion is spotted, the adult is of uniform coloration. Color of fossils. — Recent organic calcium carbonate, such as occurs in shells and corals, is white, except for the occa- sional presence of a pigment or epidermis ; Tertiary shells are darker, while those from the Paleozoic are, as a rule, darkest. Likewise, whereas many recent shells are lined with mother-of- pearl, very little is found in pre-Mesozoic shells. These changes are due to one or more of several causes. The chalky aragonite becomes changed to the darker calcite. As the pores and inter- stices become filled with some foreign substance light is excluded and a darker color results. If the inclosing sediment is dark in color, the fossil will be stained by it more and more deeply according to the length of time inclosed. A secondary replace- ment by calcium carbonate may likewise be accompanied by foreign impurities, such as carbon or iron, and thus produce a darker color. Hence the older the fossil, the greater is the prob- ability, as a rule, of the shell being dark. This generalization holds true too for vertebrate and arthropod remains, though here the increasing dark color is mostly due to carbonization. The process of fossilization likewise rapidly destroys the epi- dermis and the pigment present on many shells. Very little pigment remains in pre-Cretaceous shells. Where shells are light colored and originally had color bands, such are apt to be preserved in fossils as dark bands. Fossil objects due to inorganic agencies. — Many objects due to inorganic agencies are often called fossils. It is in accordance with general usage, however, to reserve this name for those objects having some relation to an organism, but the word fossil may be conveniently used as an adjective before objects due to inorganic agencies, such as ripple marks, to show that they have been preserved in the earth's strata. On the mar- ginal flats of an ocean may be formed and preserved marks of INTRODUCTION 21 s^^M ripples, cracks in the mud due to drying, imprints of rain drops, flows of mud due to an excess of water, and the marks showing the upper limit of the waves. But it is especially upon the mud flats of an aggrading stream or of temporary lakes, especially in the drier regions of the country, that very many and perfect ripple marks, mud cracks, and rain-drop imprints are formed and stand best chance of preservation. Such are the very regions where organic remains stand very slight chance of pres- ervation, for the periodic removal of the water causes the rapid oxidation of all lifeless organic matter, so that the principal fossils present in such strata are tracks, trails, and burrows. Distortion of fossils. — In the bending, twisting, slipping and crushing of portions of strata usually consequent upon upheaval of great thicknesses of sediment from a region of deposition to a region of erosion, more or less distortion of the included fossils must occur. At times, merely the great weight of the overlying sediment causes distortion. So it is necessary to criti- cally examine the fossil and, if possible, compare it with others of the same species to fully determine its original shape. Pseudo-fossils. — The slipping and twisting of strata likewise produce forms that at times closely resemble organic remains. These pseudo-fossils are especially noticeable in metamor- phic rocks. The slipping of one rock face against another along a fault plane produces slickensides which are often closelv similar to the Carbonif- erous plant, Cordaites, or at times to Calamites ; but the surface of a fossil will be parallel to the lamina, whether it is the organism itself or its external mold since it could normally have been deposited only in a position Fig. 6. — Dendrite (X 15), a branching incrustation, usually of manganese oxid. It reveals its inorganic na- ture in the complete ir- regularity of its branching. Drawn from the fractured surface of a Pleistocene shell. 22 AN INTRODUCTION TO THE STUDY OF FOSSILS parallel with the bedding of the strata, whereas the slickenside will be seen usually to cross successive laminae or even beds. Sometimes fractures, especially in dense, fine-grained rocks, re- semble the external molds of pelecypods or other bivalve shells. An inorganic form very often mistaken for true organic remains is the dendrite (Fig. 6) ; this branching incrustation, formed usually of manganese oxid, is common, either inclosed, as in the moss agate, or merely as surface markings. It looks much like a piece of moss or fern, but there is no regularity in its method of branching, whereas an organism always exhibits a regularity, a symmetry. Collecting fossils. — In compact, semicrystalline rocks the fossils upon an exposed surface, especially under a residual clay, are apt to become silicified, and hence when entirely weathered out of the rock they form ideal specimens. This weathering out of the entire compact fossil is especially characteristic of shales, shaly limestones, and of marls, consolidated or uncon- solidated. Hence excellent places for collecting fossils are along weathered rock surfaces, water courses leading from such rocks, or even in plowed fields, especially immediately after a rain. Index fossils. — Every fossil is more or less an index to the age of the rock in which it occurs, for it is a relic of the life which inhabited the earth when that sediment which now forms the inclosing rock was being deposited. It was early observed that succeeding rocks contain different fossils, that as they were followed from the lower to the higher beds, the inclosed fossils changed. At present the succession of life in general upon the earth is known, though more and more of its details are being discovered each year. It is known that these successive faunas and floras follow each other in the rocks the world over in approximately the same order. It has been observed that each fossil is not of equal impor- tance as an index to the age of a rock ; some species, such as the brachiopod, A try pa reticularis, occur in the strata of two INTRODUCTION 23 periods, while others are confined to a very small portion of one ; that is, some have a great and others a limited vertical distribution or time endurance. Some are confined to the strata of a single locality, while others, such as the brachiopod, Produdus semireticulatus, occur in strata of similar age over the world; that is, some have a wide and others a limited horizontal distribution or geographic range. The best index fossils are those which combine a wide horizontal with a limited vertical distribution. The study of Index Fossils is thus of great importance in determining the age of strata, for the making of geological maps and sections, working out faults, etc. Migration, etc. — ■ Fossils tell us of the body of water in which the rocks inclosing them were laid down, — whether shallow or deep, near to or far from land, open sea or inclosed basin. They tell us of changes in climate. They tell us of the presence of land barriers where now are none, of land bridges that formerly united lands now long separated. This knowledge of ancient geography that they give us is based upon the observed fact that species migrate. The larvae of beach- dwelling creatures are carried by tide and waves along the edge of the sea and thus colonize new areas. Large bodies of water, however, few animals can cross, and hence, when the same species of the trilobite Trinucleus, for example, is found in Ordovician deposits of both Europe and America, we must assume a continuous beach line, a land bridge between the two continents at that time. Mammals migrate by walking and swimming, but they, too, are limited in range by broad areas of water, high mountain ranges, etc. Thus the same species of elephant in the Pleistocene strata of both Europe and America indicates a land bridge at that time. An example of the rate of speed at which a species may migrate is found in the record of Littorina littorea, the common periwinkle. It is very abundant on the rocky shores of Eng- land. Since it does not occur in. the fossil state, or in any of 24 AN INTRODUCTION TO THE STUDY OF FOSSILS the prehistoric shell heaps in America, it is evident that it was introduced from Europe about the middle of the nineteenth century, for it was recorded from the Gulf of St. Lawrence in 1850. Thence it slowly spread southward along the coast, probably by the transport of its larvae by the southward-flowing Greenland current. In 1870 a few were noted on the Maine coast; in 1872 it was found at Salem, in 1880 at New Haven, and in 1891 as far south as Delaware Bay. In each locality where observed it had become the most abundant gastropod within two or three years after its first appearance. On the New England coast it covers the rocks and seaweed between tide limits. Naming of organisms. — In early times, only variable com- mon names or a single technical name was applied to a species of animal or plant; more often the name was long and descrip- tive. This procedure was first changed by the great Swedish naturalist, Linnaeus (or Linne), who introduced the binomial, or two-name, method. His great work (" Systema Naturae '') was published in 1735 ; this was in Latin, the scientific language of Europe at that time, hence all his technical names have Latin or Greek endings. This use of Latin and Greek was found so satisfactory, since the same names could be used by all nation- alities and languages, that it now governs the naming of fossils the world over. The generic name is usually taken from the Greek and the specific name from the Latin language. As a result the technical name of an organism, fossil or living, is the same whether used in English, German, Russian, or Japanese works. Before Linnaeus, the single technical name was often modi- fied by a descriptive phrase ; for example, one of the lady bugs was called the Coccinella with the seven black spots ; this Linnaeus called Coccinella septem- punctata. The first of the two names is that of the genus and represents the broader relationship, the second is that of the species and includes all individuals which are almost exactlv similar ; this likewise INTRODUCTION 25 follows the Latin order of names, the family name being placed first and the individual name last. The ancient Romans would not have said John Jones, but Jones John. Composition of the hard parts of organisms. — The compo- sition of the hard parts varies considerably in different organ- isms and consequently causes a variation in the preservation of the different forms as fossils. For example, percolating waters dissolve aragonite with great ease, but have little effect upon chitin. The following list contains the mineral composition of the hard parts of the more important animal and plant classes : Animals. — i. Lime carbonate: Foraminifera (most); sponges (some) ; Hydrozoa (some) ; corals (most) ; MoUus- coidea (most) ; mollusks (most) ; Echinodermata (all). a. Calcite (CaCO.3) : Foraminifera (vitreo-calcareous forms, such as Globigerina) ; corals (many) ; sponges (Calcarea) Bryozoa (most) ; brachiopods (all except the phosphatic ones) worms (Serpula, etc.) ; Crustacea (calcareous part of skeleton) Pelecypoda (many entirely of calcite, as Pecten, Ostrea ; many with only outer layer of calcite and inner of aragonite, as Mytilus, Unio) ; Gastropoda (feW; as Scalaria ; some, as Patella and Lit- torina, have only outer layer of calcite) ; Cephalopoda (few, as Argonauta and Belemnites) ; Echinodermata (all) ; hens' eggs. h. Aragonite (CaCOg) : Foraminifera (probably most por- cellanous forms, as Peneroplis) ; corals (Madreporaria) ; most scaphopods, pelecypods, gastropods, and cephalopods. Calcite and aragonite have the same composition (CaCOs) but crystallize in different systems. Aragonite crystallizes in the orthorhombic system ; in shells it usually has a chalky, opaque appearance and is compact throughout. Calcite crys- tallizes in the hexagonal system ; in shells it is usually translu- cent, with a compact surface but porous interior. In carbonic acid it dissolves more slowly than aragonite and hence when subject to percolating waters persists longer. In Mytilus ediilis, the outer layer of the shell is of calcite, the inner of aragonite ; 26 AN INTRODUCTION TO THE STUDY OF FOSSILS many of these shells from the Pleistocene have the calcite pre- served but the aragonite dissolved away. Hence it is seen why shells of brachiopods are better preserved fossils than those of mollusks. Calcite may be distinguished from aragonite by the following simple method : powder the substance and boil one minute in dilute cobalt nitrate ; if it is aragonite the precipitate will be of a pink or lilac color ; calcite, even with longer boiling, w^ill remain white (or at times somewhat yellowish from the presence of some organic substance) . 2. Silica. — Radiolaria (most) ; sponges (Silicispongiae ; this order contains most of the fossil and many of the recent sponges). (Silica (SiOo), in the form of quartz, is one of the most stable of minerals, but when secreted by an organism it contains some water, is glassy and isotropic, i.e. is penetrated by light and heat equally in every direction ; in this condition it is dis- solved with comparative ease by percolating waters containing alkali.) 3. Chitin (C15H26N2O10). — Foraminifera (few); sponges (CeratospongicT) ; Hydrozoa (most, Leptolinae and Grapto- lithida) ; corals (axis of sea-fan, etc.) ; arthropods. (The word chitin is here used in a general sense and does not imply a chemical and structural identity with the true chitin of the Arthropoda.) 4. Lime phosphate. — Brachiopods (a few, as Lingula, etc.) ; vertebrates (about 40 per cent of the ash of bones is phosphoric acid) . 5. Cellulose (CeHioOs). — Protozoa (a few); ascidians. Plants. — I. Cellulose (CeHioOs). — All plants from the thal- lophytes up, with a few exceptions. 2. Silica (SiO^). — More or less silica is present in the cell walls of diatoms, equisetes (horsetails), Carex, margins of grass blades, etc. It is especially abundant in the diatoms, the form of the plant being retained by it after the burning away of the organic matter. INTRODUCTION 27 3. Lime carbonate (CaCOs). — -Many algae, as Corallina of- ficinalis (a red alga) which it thickly coats with the white deposit, Lithothamnion (a red alga) and Halimeda (a green alga) both of which are most important in the building up of coral reefs ; also the fresh-water alga, Chara, the principal agent in the for- mation of marl. 1. Distinguish between organic and inorganic matter. 2. What is protoplasm ? 3. Give three differences between plants and animals. 4. What are the two chief conditions for the preservation of an organism in the fossil state ? 5. Name three kinds of deposits in which organisms may become buried and thus preserved. 6. What is amber ? loess ? 7. Draw a diagram illustrating terrestrial and seashore deposits and indicate the most favorable of all localities for the preservation of fossils. 8. Mention an example of a recent flood plain deposit in the United States; of -a fossil flood plain. What kinds of fossils are we most apt to find there ? 9. Give an example of a fossil lake deposit and the kind of fossils for which it is noted. 10. Define and classify fossils. 11. What are the chief minerals concerned in fossilization ? 12. How^ may the entire bodies of animals at times be pre- served ? 13. Describe the process by which {a) a leaf is preserved and fossilized ; {b) a clam shell ; (c) a bone ; {d) the burrow of a worm ; {e) a jelly-fish. 14. Explain by diagram the formation of an external and an internal mold ; of a cast. 15. Why does an injury to the mantle affect the shell? 16. How may we judge of the shape of a vertebrate animal merely by its skeleton ? 17. What changes in color does a shell undergo during fossili- zation ? 18. Mention three examples of "fossils" due to inorganic agencies ; three of pseudo-fossils. 19. What are index fossils? Describe their bearing on geo- logic and evolutionary problems. 28 AN INTRODUCTION TO THE STUDY OF FOSSILS 20. How do animals migrate ? 21. Name three groups of animals whose hard parts consist principally of lime carbonate. 22. Give an example of a siliceous skeleton ; of a chitinous. 23. What is the most usual hardening substance of plants? 24. Mention two plants with siliceous hard parts, two with calcareous hard parts. PLANTS The continued existence of such life as is familiar to us depends upon the acquirement of external energy. At the sur- face of the earth the most available source of energy is the sun's rays. Acting through the chlorophyl, — the green coloring mat- ter of plants, — this energy of the sun breaks up the inorganic components of earth, air and water into their separate elements and then recombines them into the potential or stored-up energy of foodstuffs. Plants expend this energy largely in reproduction, — in the development of spores and seeds. Animals, on the other hand, make use of this energy stored up by the plants, expending it in free movements as well as in reproducing their kind. In the lowest divisions of each kingdom, however, — 'the thallophytes of the plants and the protozoons of the animals, — still occur individuals, such, for example, as the protozoon, Euglena, which combine both methods of energy getting. The food of plants consists principally of inorganic salts and carbon dioxid in solution in water; this is absorbed by the protoplasm of the plant. In the case of the unicellular plant, the whole plant body surrounds the food and absorbs it, while among higher plants the roots and rootlets are differentiated to perform that function. In higher plants the taking up of excess liquid, or the contraction of the intaking cells, forces this food solution up through tubes which are arranged in bundles (vas- cular bundles). Under the influence of the sunlight the carbon dioxid is broken up into the gases carbon and oxygen ; the former after being combined with the inorganic substances is transferred to the growing parts of the plant through other tubes in the vascular bundles, while the oxygen is thrown off. Parasitic plants, such as the fungi and bacteria, are exceptional in that 29 30 AN INTRODUCTION TO THE STUDY OF FOSSILS they absorb the food directly from the host, either plant or animal, which has manufactured it. In respiration plants take in air through small openings (stomata) which are especially abundant upon the leaves. The use made of the oxygen is shown in the rise of temperature and in the energy of growth. Since respiration is in plants as well as in animals a breaking down process, a waste product, — carbon dioxid, is thrown out. Reproduction among plants may be either sexual or asexual. Asexual plants reproduce either by simple division, as among the bacteria, or by merely detaching single cells from themselves, as among certain algae ; each of these detached cells, called in the latter case a spore, is capable of developing without fer- tilization into an independent plant. In sexual reproduction the plant likewise separates from itself certain single cells, but these cells lack the power of developing by themselves ; be- fore growth can occur each must unite with another cell, either from a separate plant or from different parts of the same plant. The larger of these complementary reproductive cells in the higher plants contains the egg and is the female ; the other cell, which may or may not be free-swimming, contains the male element. In ah except the seed-plants the presence of external fluid water is a necessity, otherwise the male cell cannot travel to the female and produce fertilization. Plants as indicators of climate. — Plants, at least the later ones, are excellent criteria of climatic conditions; their ina- bility to migrate under the stimulus of the annual alternation of cold and warm, wet and dry seasons makes them more valuable than animals as geologic thermometers. But that in the Mesozoic, and especially in the Paleozoic, geographic dis- tribution was as sharply limited by climatic environment as now is unlikely. Some persistent primitive types such as the common brake (Pteris) w^hich thrive in both temperate and tropical regions are suggestive in this connection. The world- wide distribution of the ancient floras was mainly due to their PLANTS 31 primitive and generalized structure ; but it should not be over- looked that the ability to endure climatic variation may haye been well developed, and supplied a highly important factor in that cosmopolitan distribution which is so sharply marked from the appearance of the earliest land plants down to Upper Jurassic time. Preservation of plants. — There are of necessity many gaps in the record left by the vegetation of past ages. The early plants were soft and perishable. Moreover, it is predominantly water life — the life of the sea beaches and the inland lakes and swamps — which has been preserved in the fossil state, since land conditions favor decomposition and destruction and do not fur- nish the conditions necessary to fossilization. It must accord- ingly be only a very incomplete idea of the past vegetation of the earth that fossil plants can furnish. Despite, how^ever, the exigencies of fossilization all the great groups of plants — thal- lophytes (algae, fungi), bryophytes (mosses, liverworts), pteri- dophytes (ferns, horsetails, club-mosses), and spermatophytes (gymnosperms, angiosperms) — have left a fossil record of the larger outlines of their past history. Plant evolution has not been uniform and there are many cases of retrogression, as in the club-mosses and horsetails, yet in general a higher group has succeeded a lower one, the latter not disappearing but falling into the background. Following the early Paleozoic, or age of seaweeds, spore-bearing plants and primitive gymnosperm.s dominated in the Upper Paleozoic. More modern gymno- sperms and the cycadaceous or proangiospermous types made up the still cosmopolitan forest facies of early and mid-Mesozoic time, while from the Cretaceous to the present the angiosperms have been the leading type. It must be borne in mind that the study of fossil plants is fully fifty years behind even that of fossil vertebrates. This study, however, is being aided by the discovery of new chemical methods for the examination of carbonized remains and by the appUcation of petrography to this field. Above all, existing 32 AN INTRODUCTION TO THE STUDY OF FOSSILS knowledge of various plant forms is being constantly supple- mented by discoveries of petrified plants in all stages of growth and with their various parts, such as leaves and stems, still c<^nnected as in life. Consideration of these advances of paleobotany indicates that the plant record may soon come to have all the importance in the study of climate, former geographic relationships and evolution that the animal record has. Plants are divided, mainly on the basis of their method of reproduction as well as the accompanying development of sup- porting tissue, into four large divisions: — Page Division I. Thallophyta 32 II. Bryophyta 42 III. Pteridophyta 44 IV. Spermatophyta 55 DIVISION I, THALLOPHYTA The thallophytes include the most primitive plants, ranging in size from single microscopic cells to seaweeds of enormous dimensions. The forms included in this group agree in their simple structure, being plants in which there is usually little or no differentiation of organs, such as stems and leaves. Such a simple plant body is called a thallus, and the plants distin- guished by possessing this undifferentiated mass of cellular tissue are called the thallophytes or thallus plants (> Greek phyton, a plant). The Thallophyta include the following five sub-divisions : — Page A. Myxomycetae 2,0 B. Schizophyta 33 C. Diatomeae 34 D. Algae 35 E. Fungi 40 THALLOPHYTA SUB-DIVISION A, :^IYXOMYCET^ 33 The slime-moulds are sticky masses frequently occurring on decaying logs and leaves in a forest. They so combine the characters of plants and animals as to make it doubtful with which they should be classed. They live upon decaying organic matter, have active locomotion, and possess no chlorophyl, but they are terrestrial (sub-aerial) in habit and reproduce by spores which are very much like those of certain fungi. They possess no parts capable of preservation after death, and are not known in the fossil state. SUB-DIVISION B, SCHIZOPHYTA One-celled plants reproducing by simple division into two more or less equal parts, hence called fission-plants. They are sub- divided as follows, — 1. Bacteria. ^One-celled plants, jo^^o^ inch or less in dia- meter. These are of great economic importance as agents of fermentation, decay and disease ; they are now the chief agents in the decomposition of organic matter and unquestionably were similarly active in disintegrating the dead vegetation of past ages, as is indicated by fossil evidence. Certain fossilized plant tissues of the Pennsylvania coal-beds show a destruction of cell w^alls which has been ascribed to this cause. But for their activity it is probable that ancient plant and animal remains would have been preserved in greater abundance. 2. Blue-green algae. — Unicellular plants, occurring in slimy masses in the presence of damp, decaying organic matter. When present in enormous numbers they often produce a discolora- tion of the water, as in the Red Sea. Some are lime-secreting and thus are important as rock builders. To their agency, for example, is due the formation of oolite grains on the shores of the Great Salt Lake, the Red Sea, and elsewhere ; these grains are blow^n landward into dunes and thus form continental depasits, Oscillatoria is a blue-green alga which is one of the D 34 AN INTRODUCTION TO THE STUDY OF FOSSILS forms responsible for the hot springs deposits in the Yellow- stone Park. The origin of many of the oolites of the Jurassic of England, — Superio'r, Great oolite, etc., — has been referred to these algae as has likewise that of the oolites of the Bunter sandstone (Triassic) of Germany. SUB-DIVISION C, DIATOME.E The diatoms are a group of thallophytes with possible kin- ship with the algae. They are microscopic, one- celled plants, inclosed in two valves of which one overlaps the other. This cell wall is impregnated with silica and hence forms a resistant skeleton (Fig. 7). Reproduction is either asexual, through division of the cells, or sexual, through union of two cells to form a new individual. Diatoms occur in both fresh and salt water as well as in damp soil. In the ocean they form a large part of the plankton, — the drifting mass of organ- isms at the surface of the water, and furnish the food of many marine ani- mals. So great is their abundance that their skeletons, cast off at death or in the process of reproduction, form on the ocean bottom or on the bottom of ponds or marshes deposits of siliceous earth, — the diatomaceous ooze. Such deposits are known from the Jurassic to the present, especially in the Miocene of California and of the Atlantic coastal plain. One such deposit between the Santa Yuez and Los Alamos Valleys, Cali- fornia, reaches a thickness of forty-seven hundred feet. Fig. 7. — Examples of the silica-secreting algae, dia- toms, abundant in the ocean covering eastern Maryland during the Miocene (Calvert) times. A , Coscinodiscus lineatus Ehrenberg, a circular species. B, Sceptroneis caduceus Ehrenberg, a lanceolate species. Each X 170. (From Boyer.) THALLOPHYTA 35 SUB-DIVISION D, ALG^ The seaweeds are primitive, water-dwelling plants, ranging from microscopic, one-celled forms to large and complex plants. They show an advance over some other groups of the thallo- phytes in the presence of the green coloring matter, — chloro- phyl, which is, however, in certain of the algae masked by brown or red pigments. There is great variety in the method of reproduction. It may be either asexual through the production of special cells, — the spores, which later develop into new plants, or sexual through union of male and female cells. Upon other structural and reproductive characters coupled with the difference in color is based the classification into green, brown, and red algae. Algae have been recognized from the pre-Cam- brian to the present. I. Green algae. — Common examples are: — a. Spirogyra, the common green alga floating on ponds where its long green threads form the frothy masses called pond scum. h. Halimeda, a lime-secreting alga of modern seas. It grows on coral reefs, connecting dead coral masses. It forms exten- sive lim.estone deposits in the lagoons of coral atolls, as in the Funafuti reef. The analysis of the plant, which gives over 90 per cent of lime (CaCOs) and only 3 jq per cent of organic matter, shows its importance as a rock builder. c. Chara (stonewort). (There is a growing tendency to re- move Chara from the green algae and to raise it into a distinct group.) This plant inhabits fresh w^ater lakes of the temperate region. It secretes lime with w^hich it encrusts its leaves and stems, making them white and brittle. Upon the death of the protoplasmic part of the plant, this lime deposit disintegrates and settles as a Hmy mud, the marl of marl ponds. Chara is responsible for many fresh water limestones of the past. Char- acteristic spore cases occur in the mid-Devonian at the Falls of the Ohio and in the Hamilton of Missouri, and it is well known since the Upper Jurassic. It was especially abundant in the 36 AN INTRODUCTION TO THE STUDY OF FOSSILS Tertiary. On the Isle of Wight there are considerable deposits of Oligocene fresh water limestone which are rich in remains of Chara. 2. Brown algae. — Examples are : — a. Fucus, the rock weed, common on rocks exposed between tides. h. Laminaria, the large alga, devil's apron, etc., growing in the deeper water beyond the low tide limits (Fig. ii, A). This marine genus includes the largest plants known, some having huge trunk-like stalks and reaching a height of several hundred feet. c. Sargassum of the Sargasso seas. d. Nematophy- cus, a large plant w^hose fossilized stems have been found in the Silu- rian and Devonian of Europe and America. In some respects it resem- bles the big Lami- narian seaweeds of the present, though its exact relation- ship cannot be de- termined since its microscopic struc- ture is not pre- served. There are no im- portant lime-secreting genera among the brown algae. B Fig. 8. — A marine lime-secreting alga, Primicorallina trentonensis Whitfield, from the Trenton limestone (Middle Ordovician) of New York. Much of the limestone where it occurs is made up of its remains. A, a specimen showing the whorled arrangement of the branchlets of the second order at a and those of the third order at b. B, restoration of the entire plant. (From Ruedemann.) THALLOPHYTA 37 3. Red algae. — The lime-secreting types of these algae are the " nullipores " or " corallines." They include among others, — a. Corallina. This plant grows in delicate jointed filaments which form little tufts on rocks and seaweeds in tide pools along the northern Atlantic Coast. The white incrustation of its fronds gives it a coral-like appearance. Primicorallina is a distantly related form from the Ordovician (Fig. 8). b. Lithothamnion. This usually forms crusts on the surfaces of shells, corals and rocks (Fig. 9, C). On the coast of Spitz- bergen, for example, it covers the bottom in deep layers for many Fig. q. — Comparison of the ancient Cryptozoon with the modern alga, Lithotham- nion. A, Cryptozoon bassleri Widsind ( X ^), from the Cambrian of Pennsyl- vania. The vertical transverse section shows the successive laminae of growth. B, Cryptozoon proliferum Hall, from the Beekmantown (Lower Ordovician) of Pennsylvania. The transverse section ( X 6) shows what may be spore cases {s.c). C, Lithothamnion living off the coast of Eastport, Maine. The vertical transverse section ( X I2) shows the growth laminae and the spore cases. {A and B after Wieland.) miles, the material for future strata of the earth's crust. Some globular arctic species reach a diameter of six to eight inches. 38 AN INTRODUCTION TO THE STUDY OF FOSSILS Lithothamnion has been one of the principal reef builders since the Cretaceous. c. Here also may probably be placed such early Paleozoic calcareous masses as Cryptozoon (Fig. 9). Lime secretion. — It is in the securing of carbon from the decomposition of CO2 for the building of their tissues that algae secrete lime. Land plants derive the CO2 from the air. Aquatic plants must secure it from the water. An excess of CO2 in the water holds lime carbonate in solution, and when the CO2 is abstracted from the water by the plants, the lime is of necessity thrown down, and thus is deposited in or upon the tissues of the plant which caused its precipitation. Algae as rock-builders. — Algae have been found to be in many cases, at least, the most important lime contributors to the up- building of the coral reefs, much more important than the corals themselves. A boring in the atoll of Funafuti penetrating to a depth of 11 14.5 feet showed that in the composition of this typical " coral-reef " the order from most to least abundant of the most common organisms is as follows : i . Lithotham- nion ; 2. Halimeda; 3. Foraminifera, a lime-secreting order of Protozoa; 4. Corals. All these occurred from top to bottom of the boring. Thus in the formation of this atoll nuUipores were found to be the most important agent. This is true to a greater or less degree of many other " coral-reefs " of the Pacific Ocean, also of the East Indian and West Indian waters and the Mediterranean. Of these nullipores, Lithothamnion grows abundantly at a depth of two to three hundred fathoms; it also occurs in waters far from the tropics; off the coasts of Spitzbergen and Nova Zembla it covers the bottom in water of ten to twenty fathoms. The growth of nullipores may be faster than that of corals since they often cover and smother liv- ing colonies of the latter. Lime-secreting algae are thus seen to be of vast geologic importance in the formation of limestones since they grow so rapidly and at such various depths and temperatures. But evidences as to the nature of the organisms THALLOPHYTA 39 which build the Umestone may be destroyed. The studies of J. Walther on a Lithothamnion reef at a depth of one hundred feet in the Bay of Naples have shown that the action of percolat- ing water may obliterate all the structure of the seaweed, leav- ing a structureless limestone. Many examples of such structure- less limestones are known from the Mesozoic and Cenozoic rocks of southern Europe in some of which a few specimens of Lithothamnion are still preserved. Thus it may not always be possible to tell in the study of any given limestone what organ- isms were operative in its upbuilding. In those cases, however, where the species can be recognized, calcareous algae are often valuable as index fossils since there are certain forms with re- stricted geological, but wide geographical, range. Such, for example, is Solenopora compacta, abundant during the middle Ordovician in Canada (Trenton and Black River formations), in Scotland (Llandeilo-Garadoc), and in northern Europe. It often forms entire beds of limestone ; at times it weathers out as little pealike masses. Fossil banks of calcareous algae are believed to be responsible for certain structures in the Bighorn dolomite of Wyoming. Other fossil reefs on a gigantic scale are now represented, according to many geologists, by the dolomites of the southern Tyrol. Certain algae, the thermal algce, are responsible for the beautiful siliceous and calcareous deposits of the Yellowstone Park. In some way not wholly understood they cause the depo- sition of the calcium, as at Mammoth Hot Springs, or of the silica, at most of the other hot springs. The beautiful colors of these deposits are hence due to plants, — plants which here live in water of a very high temperature, — between 90° and 185^ F. The kind and color vary with the temperature, there being representatives of the green algae, the blue-green, etc. In the cooler w^aters these forms may be recognized as algae, appear- ing in green filaments, or red or brown leathery sheets lining the springs and resembling the seaweeds of the coast. But in the 40 AN INTRODUCTION TO THE STUDY OF FOSSILS hotter springs the masses become so densely gelatinous, or so thickly encrusted with silica, as not to be easily recognized. Doubtful algae. — It has been shown that many fossils which were formerly described as algae are not plants. Some are the molds of burrows or tracks of animals and some are of inor- ganic agency, such as Oldhamia from the Cambrian of Ireland, formerly considered the oldest of all vegetation and now ex- plained as merely the wrinkhng of the slate due to pressure. The " Cockstail alga " (Taonurus cauda-galli) which occurs in great abundance in the " Cauda galli grits " (Esopus) of the Middle Devonian of New York, and Arthrophycus harlani, abundant in the Medina sandstone of the Silurian, are at present generally regarded as the burrows of sedentary chaeto- pod worms. SUB-DIVISION E, FUNGI These plants are especially distinguished by the absence of chlorophyl. They are thus unable to manufacture starch and sugar from the soil and air and must live on that already manu- factured, — that is, upon other organic matter. Accordingly they live either as saprophytes upon decaying organic matter or as parasites upon living organisms. Instead of possessing the more complex structure of chloro- phyl-bearing plants, a fungus consists essentially only of a branch- ing mass of threads called the mycelium. These threads pene- trate the cell walls of their ''host," — plant or animal, — and live upon its substance. Toadstools and mushrooms, molds, mil- dews and yeast are common examples. As would be expected from their structure, fungi are rarely preserved as fossils. Mycelium threads of a fungus have been detected under the bark of Sigillaria from the Pennsylvanian coal-beds, and there is evidence that even as far back as the Si- lurian, fungi preyed upon "shell-fish," since certain brachiopod shells are found more or less perforated by fine tubules which in some cases end in spherical sweUings. These borings (Fig. lo) THALLOPHYTA 41 They are dry, are probably the work of the mycelia of a mold-like fungus (Phycomycete) . Lichens are thallophytes of wide distribution gray and brown fronds spread- ing over tree trunks and rocks. They represent a union of algae and fungi, since each lichen is actually made up of a fungus and an alga, li\'ing together in the mutually helpful relationship which is called symbiosis. The threads or mycelium of the fun- gus interweave among the cells of the alga, and while the fungus is dependent upon the foods manufactured by the alga, it aids the latter by the protection which its threads afford and by the water which it takes up and holds. Fossil lichens have been recognized only from very recent formations. . Fig. 10. — • A fungus penetrating an impunctate brachiopod shell on one side only. The round swellings were probably spore sacks. This fungus from the Clinton (Silurian) of Rochester, New York, is proba- bly a member of the Phycomycetes. X 250. (After Loomis.) 1. What is the source of the energy of plants ? Of animals ? 2. How do plants eat? Respire? 3. What difference between the gametophyte and sporophyte phases from algse to seed-plants ? 4. What significance has this in theories of plant evolution ? 5. Compare plants and animals (i) as indicators of climate ; (2) as to likelihood of preservation as fossils. 6. Give the four large divisions of plants with the geologic range and the significance of the name of each. 7. What distinguishes the thallophytes? 8. Give distinguishing characters of the five sub-divisions with known geologic range and examples of each. 9. Upon what is based the division of Algae into green, brown and red groups ? Give examples of each. 42 AN INTRODUCTION TO THE STUDY OF FOSSILS 10. How do plants secrete lime ? 11. Name the important lime-secreting groups of Algae with two genera under each. 12. How important are Algae as rock-builders? 13. What are lichens ? Their geologic age ? DIVISION II, BRYOPHYTA The Bryophyta exhibit a distinct advance upon the Thallo- phyta in the greater soecialization of the plant body and in the different method of reproduction. As the algae are essentially water-dwelling plants there is little necessity for specialization of organs since any of the plant's cells can serve for absorbing the food which surrounds it on all sides. With the evolution of the bryophytes there came a change from aquatic to terres- trial conditions and there thus arose the need for specialized organs adapted to getting the food from the soil and from the air. The adaptation to terrestrial conditions being still imper- fect, however, many of the bryophytes, such as some of the liver- worts, still have thalloid plant bodies, w^ithout distinction of root, stem and leaves, wMe the group as a whole is moisture- loving (Fig. 11). The most distinct advance, however, of the bryophytes upon the thallophytes is in the method of reproduction, — in the estab- lishment of a distinct alternation of generations. This method is illustrated by the life history of some common moss, such as the hair-cap {Polytrichum commune, Fig. 11, C). This plant, as we commonly see it, consists of a green stalk bearing many tiny leaves, and, if the plant is fruiting, it supports at its apex a slender bristle-like seta which ends in a sac (capsule) containing spores. When the spores fall on moist earth they may ger- minate by sending out a mass of green threads, the protonema, and from this grow the tiny moss plants. These plants bear the male and female reproductive organs and from the union of their products, — the fertilized egg cell, arises the spore-bearing part of the plant, i.e. the capsule borne at the summit of the seta. Thus there is an alternation of the asexual or sporophyte BRYOPHYTA 43 /^vS^ b E Fig. II. — Diagram to show the increase in prominence of the sporophyte stage of plant life from the alg« to the higher seed-plants. Among the thallophytes, both the sexual and asexual methods of reproduction are repre- sented. A illustrates the asexual, wherein certain cells of the plant divide into smaller cells, — the zoospores, which, without union with other cells, develop directly into new plants. B-E' illustrate the sexual method effected through an alternation of genera- tions, wherein a vegetative stage — the sporophyte — alternates with a reproductive stage — the gametophyte. The gameto- phyte stage of the various forms is below the line a-h, the sporophyte stage above it. The size of the plants in the diagram bears no relation to their size in nature. This diagram need not imply that the seed-plant has been evolved from the algae successively through the mosses, etc. ; the fern may have evolved directly from the algae. Any direct fossil evidence in favor of either line of evolu- tion is wholly lacking. A, the marine alga, Laminaria saccharina, the devil's apron. B, the very common liverwort, Marchantia polymorpha. B' , same, with the tip of one of the umbrella-like lobes magnified. C, the hair-cap moss, Polytrichiim commune. D, a very young sensitive fern, Onoclea sensibilis. E, the elm tree, Ulmus americanus. E', same, with the gametophyte stage enlarged (see p. 77). Among the bryophytes, B and C, the gametophyte is the prominent stage. This is the common liverwort or moss plant which bears the sporophyte ; this latter remains attached to and dependent upon the gametophyte throughout its whole existence. In the pteridophytes, D, the sporo- phyte is the prominent, common, leafy fern plant which has become independent of the gametophyte. The latter is the true two-lobed prothallus which, though independ- ent of the sporophyte, is tiny and short-lived. In the spermatophytes, E, the gamet- ophj'te stage has become so reduced that its whole existence is passed invisibly dependent upon and within the sporophyte. p, pollen grain with its single included nucleus; p', the same at a later stage with three nuclei ; p" , the same lodged upon the stigma, with the tube cell already within the ovule ; t.c. tube cell. 44 AN INTRODUCTION TO THE STUDY OF FOSSILS stage, — the product of the union of male and female elements, and the sexiial or gametophyte stage, — the product of the ger- mination of the spores. The moss plant is distinguished b\' the predominance of the gametophyte stage over the sporophyte, since the sporophyte is only the slender stalk and its capsule, dependent on the leafy moss plant, — the gametophyte. Derivation of name. — Greek bryoii, moss, + pliyfou, plant, referring to its typical class, the mosses. The Bryoph\'ta are divided into two classes, — the liverworts (Hepaticte) and the mosses (Musci). Liverworts include the simplest br^'ophytes, with many similarities to the Algie. IVIarchanlia is a connnon example (Fig. II, B). A common moss is the hair-cap, Polyly'ichum commune (Fig. II, C). JNIosses, especially of the genus Sphagnum, have been in recent times most important agents in the formation of peat. Such mosses grow in bogs, and as they die below continue to grow above. They are mainl\- sub-arctic to cold temperate in habitat. The Dismal Swamp sphagnum is one of the most southerly deposits, occurring thirty-five feet thick. There is no fossil record of mosses and liverworts earlier than the Tertiary, though probably they are not confined to such relatively modern times. 1. Describe both stages (gametophyte and sporophyte) of a common moss plant. 2. Give two dift"erences between a thallophyte and a bryo- phyte. 3. How far back in geologic time are fossil mosses found ? 4. Name the two classes into which the Bryophyta are divided, with an example under each. DIVISION III. PTERIDOPHYTA The pteridophytes are much more complex plants than the bryophytes. While the structure of the moss plant is more or less simply cellular, that of the fern plant is vascular ; that is, PTERIDOPHYTA 45 like the higher flowering types, the plant possesses a series of vessels which form a conducting apparatus for the food and manufactured sap. Bryophytes and pteridophytes are some- times called cryptogams ; that is, plants without true flowers and seeds, in distinction to the phanerogams, or higher flow^ering plants; of these the bryophytes are the cellular cryptogams, and the pteridophytes the vascular. Like the bryophytes, the pteridophytes reproduce by a conspicuous alternation of genera- tions, but differ from the bryophytes in the relative importance of the sexual (reproducti\'e) and the asexual (vegetative) stages. In both, the better known and longer- lived part of the life history is represented by a leafy plant which alternates with a less conspicuous phase. The leafy moss plant, how^ever, originates from the spore and produces the male and female elements, while the leafy fern plant originates from the fertilized egg and produces spores. Thus, vv'hiie the moss plant is the reproduc- tive or gametophyte stage, the fern plant is the vegetative or sporophyte (Fig. 11, D). The life history of the Pteridophyta may be illustrated in general by observing the development of some fern, such as the common Christmas fern. Some of its leaves will be found to bear shorter leaflets near their ends. Upon the under side of such leaflets are row^s of small dots, the sori or heaps of spore cases. When one of the tiny spores drops to the ground under conditions where it can germinate it devel- ops into a small, flat, disk-like body, the prothallus. This bears the male and female reproductive organs and from the union of their products, the fertilized egg, growls the leafy fern plant. Thus, in ferns, the sporophyte, which is the leafy plant, and the gametophyte, which is the prothallus, are independent of each other. It has been seen that in mosses the sporophyte is depend- ent on the gametophyte, and it will be seen later that in the higher, flowering plants the gametophyte is completely depend- ent on the sporophyte. Derivation of name. — Greek pteris, a fern, + phyton, a plant, in reference to its best known order, the ferns. 46 AN INTRODUCTION TO THE STUDY OF FOSSILS The Pteridophyta are sub-divided into the following orders : a. Filicales (including Ophioglossales, which is sometimes con- sidered a distinct class), — the ferns. b. Equisetales, — the horsetails. c. Lycopodiales, — the club-mosses. d. Sphenophyllales. ORDER a, FILICALES The ferns usually possess a broad frond or leaf which is often divided into pinnae, or leaflets. The spore cases are gathered into sori, the round " fruit dots," borne on more or less modified portions of these leaves or on independent fruiting stalks. Common living examples are Polystichum, — the Christmas fern, and Onoclea, — the sensitive fern. Ferns are known to have existed from the time of the Devo- nian, and must have appeared before the close of the Silurian. Nearly all the living families have existed since the Jurassic, while at least two families, the Osmundaceae and the Maratti- aceae. have been traced back to Paleozoic ancestors. It is rare that all of the organs of any fossil plant may be described, since they are so easily separable from one another. This incomplete- ness of data is, for example, true in the case of fern-like forms. Hence until recently the characterization of many fossil genera rested solely on the form and venation of the leaf. One of the largest of these frond genera w^as Neuropteris. Fructifications later found in connection with leaves of this genus have deter- mined that this as well as many other genera with fern-like fronds is not a true fern but a member of the great group of Cycado- filicales, — an order of Pteridophyta intermediate between the ferns and the cycads. Fossil examples of true ferns are : (i) Osmundites (Jurassic to Tertiary). — Fern stems with the peculiar structure of the stem of the living Osmunda, — - the common royal fern. This relationship is suggested by the name in which the suffix ''-ites " added to the name Osmunda PTERIDOPHYTA 47 means " stony " ; this suffix is used in many names of fossil plants to suggest their kinship with modern forms. (2) Dictyopteris and Camptopteris. — Remarkably handsome forms of Upper Triassic-Cretaceous age, with lyrate fronds often three feet or more broad, and with a characteristic netted venation. C,^ I Fig. 12. — The fern, Onoclea. A, the living sensitive fern, O. sensibilis L. (X 4), from Maine ; the fruiting stalk between two sterile leaves. B, O. inquirenda Hollick ( X f ), from the Cretaceous of Long Island, New York ; the fruiting stalk. {B, from Hollick.) 48 AN INTRODUCTION TO THE STUDY OF FOSSILS (3) The sensitive fern {Onoclea sensibilis). — Now living only in eastern North America and eastern Asia, but present throughout the Northern Hemisphere during the Pliocene (Figs. II, D, 12). 1. Discuss two characteristics of pteridophytes which show them to be more highly organized plants than bryophytes. 2. Give briefly the life history of the common Christmas fern. 3. Tell how the Pteridophyta are sub-divided, giving both scientific and common names. 4. With what ferns are you familiar ? Have you ever seen a fern prothallus ? Which is the more commonly seen stage of the fern, — the reproductive or the vegetative ? 5. When, in geological time, did ferns appear? 6. Name two fossil examples. 7. Give an example of a fern which has existed from the Tertiary to the present. Has it changed much in appearance since the Tertiary ? ORDER h, EQUISETALES Living horsetails are low plants with simple or branching stems which are strongly furrowed longitudinally and are divided into sections by joints. The leaves are small papery scales, arranged around the stem in a circle at each node. In the Car- boniferous, however, representatives of this order were large forest trees and bore large leaves. These fossil remains, moreover, show that horsetails were formerly one of the most abundantly represented groups of plants, though at present the order survives in only one genus, Equisetum. The Equisetales have existed from the Devonian to the present. Apparently the last of the Calamites group, — the Paleozoic horsetails, died out at the close of the Paleo- zoic ; but in the Mesozoic the equisetes were represented by forms which were probably intermediate between the Paleo- zoic and the living horsetails. Equisetites was a very large horsetail of the Triassic with a stem eight inches in diameter and with over a hundred leaves in a whorl. Other fossil ex- amples are : — PTERIDOPHYTA 49 (i) Calamites (Figs. 13, 150). — A tree often attaining a height of one hundred feet, usually preserved in the form of casts of the interior of the hollow stem. The markings on the surface of Fig. 13. — The ancient horsetail. A, B, Calamites suckowi Brongniart, from the Carboniferous coal deposits of Pennsylvania. A, a cast of the hollow interior of a small section of the stem ( X f). B, a. portion of the surface of this in detail. C, diagrammatic cross section of a mature calamite stem to show origin of the ribs and grooves upon the cast, gr., grooves (internodal furrows) formed by the inwardly projecting ends of the vascular bundles; i.ca., casts of infranodal canals opening in the medullary rays at the nodes; m.r., medullary rays; n., nodes; r., ribs (internodal ridges) formed by the groove upon the inner surf ace of each medullary ray ; i).6., vascular bundles {A, B from Lesquereux.) these casts are the print of the inner surface of the wood and do not correspond to the ribbing of the external surface of an Equisetum. Hence conclusions establishing the relationship of Calamites to the horsetails cannot be based on the external E 50 AN INTRODUCTION TO THE STUDY OF FOSSILS appearance of most of the fossil specimens but on comparison of the internal anatomy when preserved, and on the fructification. These internal molds are marked with longitudinal ribs and furrows, and are jointed, as are the stems of the modern horse- tails. The furrows correspond to the vascular bundles. The stems branched and bore narrow, lance-shaped leaves arranged in whorls at the nodes, or joints, of the stem. A single nerve passed from end to end of the leaf. Certain cones described under various names when found separately have been found in connection with a few specimens of Calamites stems. Calamites disappeared in the Permian ; during the Pennsylvanian it was an abundant form in the coal swamps of eastern North America. (2) Annularia (Fig. 14), a smaller plant with a stem of two or three inches diameter, and abundant in the Pennsylvanian of eastern North America, is classed with Calamites as a near relative, if it is not actually in some cases merely smaller branches of that form. 1. What is the name of the only living genus of this order? Describe its appearance. 2. When in the past did this order include large forest trees? Name an example of such a tree. 3. Sketch Calamites, (i) two joints, surface view, (2) cross section. Label joint, leaf bases, position of vascular bundles. 4. Sketch Annularia; label leaflet. What is its probable relationship to Calamites ? What is its age ? Fig. 14. — The ancient horsetail, Annu- laria longifolia Brongniart ( X 2). from Pennsylvania, showing seven whorls of leaves. This flourished in the fresh- water coal swamps of eastern North America during the Pennsylvanian time. (Redrawn from Lesquereux.) PTERIDOPHYTA 5 1 ORDER c, LYCOPODIALES Living club-mosses are largely creeping, many-branched plants. Tiny moss-like leaves thickly clothe the stem while the spore-bearing leaves are arranged in club-like cones. Thev embrace but four living genera, of which the two more common are Lycopodium, — the common ground pine, and Se'aginella. These are, however, the remnant of a very impor- tant group of the Paleozoic which attained their greatest size and abundance in the Carboniferous, where they included many of the largest forest trees. They have since gradually declined pari passu with the increasing importance of the more special- ized seed plants. Lycopodiales are known from the Devonian to the present. Among their fossil representatives are : — Lepidodendron (Figs. 15, 150). — This was a lofty tree of the later Paleozoic, appearing in the Lower Devonian and dying out in the Permian ; it was especially abundant throughout the world during the Carboniferous. The trunks were straight and somewhat palm-like, attaining at times a height of one hundred feet, and bore toward the top a crown of branches. Both branches and stems always forked dichotomously. The stems were densely clothed in long, simple, pointed leaves, much like those of the pine, which sometimes reached a length of six or seven inches. When these leaves were shed, their bases remained attached to the stem, thus cover- ing the bark of the branches and even of the larger trunks with a distinctive spirally arranged ornamentation. Each of these marks of the former attachment of the leaves is rhombic in out- line and somewhat convex. It is called a " leaf-cushion." The apex of its convexity represents the scar left by the fall of the leaf, while the remainder of the rhombic area is formed by the decurrent base of the leaf which has remained on the stem. The various marks upon the leaf-cushion are the prints of various parts of the stem of the leaf. Thus the central of the 52 AN INTRODUCTION TO THE STUDY OF FOSSILS three dots on the lower edge of the scar itself is the severed end of the vascular bundle which formerly passed out through the stem into the leaf, the other two representing strands of B Fig. 15. — -The ancient club-moss, Lepidodendron modulatum Lesquereux, from the coal horizon of Pennsylvania; Pennsylvanian in age. A, surface characters of a small part of a trunk ( X i). 5, a single leaf-cushion ; natural size. I.e., leaf-cush- ion, — the entire rhombic area except the leaf scar {l.s.) and the base of the ligule {lig.) ; l.s., scar left by the fall of the leaf; lig., ligule; par., lateral strands of leaf tissu-e (the parichnos), supposedly here respiratory in function; v.b., vascular bundles, the main tubes for the transfer of sap to leaf and manufactured material back to trunk. {A from Lesquereux.) leaf tissue. The small triangular dot above the scar has been shown to mark the position of the ligule, a leaf-like organ present in Selaginella and Isoetes, living allies of Lepidodendron. Our knowledge of Lepidodendron is based upon fossilized remains of all of its parts. The large trunks have been fcund abundantly in England in such a good state of preservation that PTERIDOPHYTA 53 the cellular structure is easily observed, while the peculiar ornamentation of the surface of the stem is shown by the ex- ternal molds. In the great majority of specimens the leaf bases only are preserved ; but attached leaves have been found in some of the calcified specimens of the English " coal balls," in which whole masses of stems, leaves, and fruits are found in a wonderfully preserved condition. These coal balls are simply concretions of the carbonates of lime and magnesia .which formed around certain masses of the peaty vegetation as centers and, through inclosing and interpenetrating them, pre- served them from the peculiar processes of decay which con- verted the rest of the vegetation into coal. In them the min- eral matter slowly replaced the vegetable matter, molecule by molecule, thus preserving the cellular structure to a remarkable degree. Such balls are especially frequent in the coal of certain parts of England (Lancashire and Yorkshire). Enormous spreading root-like underground stems occur in the rocks of the Pennsylvanian, apparently in the position in which they grew. Such root-like organs, to which the name Stigmaria has been given, were possessed by both Lepidodendron and the allied genus, Sigillaria. That they are not true roots is evidenced by their anatomical structure and their habit of branching, always into two, as has been noted in the stems of Lepidodendron. They bear many small appendages which seem to be true roots. Such root-bearing underground stems are characteristic of living lycopods. These large and spread- ing root-like organs were adapted for growth in wet ground where long roots were not needed for penetrating far into the soil for moisture. It is in the fossil cones, that show its manner of fruiting, that Lepidodendron betrays its relationship to the living club-mosses. The cones of both fossil and living lycopods con- sist of scales arranged around an axis, each bearing on its upper side a large spore case containing many spores, all of one kind. These cones of Lepidodendron are known by the collective name 54 AN INTRODUCTION TO THE STUDY OF FOSSILS of Lepidostrobus, and usually occur as impressions in coal; the internal structure is well known from the study of the cal- cified specimens of the coal balls together with several silicified specimens and casts. The cones vary from an inch to one and a half feet in length. Sigillaria (Figs. i6, 150). — This was a tree which probably re- sembled Lepidodendron in general appearance as well as in geologic range. It differed in the structure of its stem and in the arrangement of leaves, as is indicated by the impressions of the bark covered with leaf-cushions. The leaf- cushions are hexagonal in out- line and arranged in quite regu- lar vertical rows. Its cones are known as Sigillariostrobus. Its underground stems have been discussed under Lepidoden- dron. 1. Name tw^o common living club-mosses. Where have you seen them growing ? 2. What is the geologic range of this order ? 3. Sketch a leaf-cushion of Lepidodendron; label, where present, scar left by fall of leaf, the decurrent base of leaf, and of vascular bundle passing into leaf. 4. Sketch (reduce in size) a foot length of Stigmaria, a small portion in detail, indicating the little ''roots." What was the function of Stigmaria? 5. Sketch a small portion of Sigillaria. How does it differ from Lepidodendron ? 6. What are coal balls? In what country and in what geological formation do they occur most abundantly ? 7. Why are the fruit, stem and roots of Lepidodendron and Sigillaria known under separate names ? 8. How do fossil lycopods resemble living ones ? Fig. 16. — Sigillaria polila Lesque- reux, from the Pennsylvanian formations of Pennsylvania, show- ing the leaf scars arranged in vertical rows. Natural size. (From Lesquereu.x.) SPERMATOPHYTA 55 ORDER d, SPHENOPHYLLALES A Paleozoic group of slender plants with jointed stems, and leaves in whorls. They were probably trailing or climbing in habit, and are known from the Devonian to the Permian. Sphenophyllum and a related Mississippian genus, Cheirostrobus, based on one of the most beautifully preserved fossil fruits ever recovered, combine to such a degree the characters of both the lycopods and the equisetes that the Spheno- phyllales are held to be the descendants of the ancient stock from which club-mosses and horsetails have diverged in the course of evolu- tion. The group became extinct at the close of the Carboniferous. Sphenophyllum (Fig. 17). — A small, branch- ing plant with slender, ribbed stems, represented by many species in the Pennsylvanian coal fields of eastern North America. Leaves usually six in a whorl and wedge shaped or cut into lobes. Thus externally it resembles a small Calamites, but the anatomy of the stem, and of the cone, show it to be different. The name from the Greek sphenos, a wedge, + phyllon, a leaf, refers to the usual shape of the leaves. 1. Has this order any living representatives? 2. Describe Sphenophyllum. 3. How is this order related to the club-mosses and the horse- tails ? Fig. 17. — Spheno- phyllum schlot- heimii Brongni- art, from, the Pennsylvanian coal deposits of Pennsylvania. Natural size. (Redrawn from Lesquereux.) DIVISION IV. SPERMATOPHYTA These include the most highly organized plants and are dis- tinguished by the production of seeds (whence the common name of seed-plants). The difference between these and the 56 AN INTRODUCTION TO THE STUDY OF FOSSILS lower groups is not, however, so great as at first appears. There is the same alternation of the vegetative (asexual) and repro- ductive (sexual) generations, the sporophyte and the gameto- phyte, as is seen in the Pteridophyta, but the alternation is less evident. Inequality between sporophyte and gametophyte is still more pronounced than in the fern. The " seed " is the beginning of the sporophyte stage; the embryo within it later unfolds into the mature plant. In specialized organs within the flower or cone there are developed the sporangia, either male or female. The female sporangium is called the ovule, and the male the anther sac. From these sporangia are discharged the spores, — the pollen from the anther sacs, a specially differentiated cell from the ovule ; these spores develop either into the male or the female gametophyte as the case may be, and from the union of their products results the fertilized ovum, — the seed. All the process of formation of the gametophyte takes place within the flower. For discus- sion of this process see page 77. Derivation of name. — Greek sprrma, seed + phyton, plant. The members of this division are distinguished by the production of seeds. The spermatophytes are divided into : Page A. Gymnospermae 56 B. Angiospermae 75 SUB-DIVISION A, GYMNOSPERiVLE In these plants the seeds are unprotected by any covering. This character is indicated by the derivation of the name from the Greek gymnos, naked + sperma, a seed. Trees and shrubs, mostly evergreen. They include the fol- lowing orders : a. Cycadofilicales. b. Cycadales : 1. Cycadeoideae. 2. Cycadeae. SPERMATOPHYTA 57 c. Cordaitales. d. Ginkgoales. e. Coniferales. f. Gnetales. Order A, Cycadofilicales A Paleozoic group of plants with fern-like leaves (Fig. 150). They were often fern-like in habit, though including likewise vines and trees. They were formerly thought to be ferns because of the form and venation of their leaves. No sporangia, however, "^ ^m^ Fig. 18 a. — Codonotheca, one of the most singular and ancient microspore-bearing fruits known. From the Pennsylvanian of Mazon Creek, Illinois. Figures 1-3 show the interior faces of the lobes covered with spores just as brought to view when the nodules in which the fruits are embedded are split open. Figures 5-6 are the spores enlarged 28 and 85 times respectively, while Y\i. 4 is a restoration of the flower-like fruit, natural size. (From Sellards.) were found on any of the leaves and hence it came to be suspected that they might not be true ferns. Stems were finally found in association with some of these leaves whose anatomy com- 58 AN INTRODUCTION TO THE STUDY OF FOSSILS bined characters of ferns and cycads. Recently true seeds have been found attached to stalks bearmg the fern-like leaflets. These plants were accordingly shown to be primitive seed-plants intermediate between the ferns and the cycads, a relationship indicated by the name applied to them. In some the cycad features predominate, in others those of the ferns. Of those fruits which may belong to this gymnospermous line, one of the most important yet discovered is that show^n in the adjoining figure iS a. It accompanies cycadofilicalean foliage in some abundance in the ironstone nodules of Mazon Fig. iSb. — Examples of the cycadofilicales (an extinct class combining characters which to-day are separated into the distinct groups of ferns and cycads). A, Neuropteris hirsuta Lesquereux ; a portion of two leaflets (pinnules, p.), with the small stipules {s.) at their base. B, an almost complete frond of N . smithsii Lx. Both (natural size) from the Pennsylvanian period of Pennsylvania. (From Lesquereux.) Creek, Illinois, and in its outer features closely resembles the fruits described in England as the seeds of Neuropteris. The full meaning of this ancient type of fructification is not yet SPERMATOPHYTA 59 understood. If, as is quite possible, it is the male flower of Neuropteris there was a much stronger resemblance between the male and female flowers of some of the cycadofilicaleans than has been supposed. Needless to say the study of such forms has a primary importance because of the direct bearing on vital problems of plant evolution and morphology. It has been estimated that the Cycadofi.icales formed fully half of the known vegetation of the Carboniferous coal deposits. Neuropteris (Fig. iSb). — This is an example of one of the most familiar of the fern-like fronds of the Pennsylvanian coal de- posits. The leaves are very large and compound, being bi-, tri-, or quadri-pinnate, with oblong leaflets which are usually attached to their common stalk by a short stem. Each bears a median nerve from which spring secondary ones. The leaves therefore are fully fern-like in superficial appearance. That Neuropteris was not, however, a true fern was suspected from the constant absence of sporangia from the leaves and this con- clusion was established by the finding of leaves of the Neurop- teris type in association with cycad-like stems bearing true seeds. Pinnules of this genus are abundant in the Mazon Creek iron carbonate clay concretions. These Pennsylvanian strata in Grundy County, Illinois, have in this manner preserved with- out crushing and in wonderful perfection not only plant remains such as Neuropteris, Pecopteris and fruits, but also crustaceans, insects and fish-bones. Pecopteris. — Fronds much like those of Neuropteris, and of similar age, but leaflets attached to the stalk by their whole width and touching one another. The small, flat-winged seeds are well known in P. plunckneti. Lyginodendron. — Stems varying in diameter from one eighth of an inch (3 mm.) up to an inch and a half (4 cm.), not branch- ing, but very long, bearing many leaves. Leaves very large, much divided and fern-like in appearance. That Lyginodendron was a climbing plant is considered likely 6o AN INTRODUCTION TO THE STUDY OF FOSSILS from the slenderness of its stem in proportion to its length and from the presence of spines on stems and leaves. Fragments of the stems and leaves of this plant occur very abundantly and in well-preserved condition in the calcareous nodules or coal balls of the English Carboniferous coal deposits mentioned above. The plant has very nearly the stem structure of a cycad, but a fern-like leaf. Highly organized seeds have been found in a definite connection with this leaf, which shows that Lyginoden- dron, instead of being a fern as was formerly supposed, was a seed-plant. It was still, however, a very primitive seed-plant for both seeds and pollen sacs were borne on slightly altered portions of the ordinary leaf. Lyginodsndron is thus seen to be a noteworthy example of synthetic types, that is, of forms that combine characters which afterward separate and distinguish separate orders. 1. What is the chief distinguishing characteristic of the Spermatophyta ? How is this indicated in the name itself ? 2. Describe the formation of the sporophyte and the game- tophyte stages in the spermatophytes. 3. Into what subdivisions are the spermatophytes divided ? 4. What is the difference between a gymnosperm and an angio- sperm ? Show that this difference is indicated in the derivation of the name. Name three common living gymnosperms. 5. Into what orders are the gymnosperms divided ? 6. What are the Cycadofilicales ? In what respect do they resemble ferns ? How are they like cycads ? When were they most abundant ? Name an example. 7. Sketch a Neuropteris pinnule. How is it known that this is not a fern ? 8. For what is Mazon Creek famous ? 9^ In what respect is Lyginodendron a synthetic type ? Order B, Cycadales Family i, Cycadeoidece. — This extinct family of trees or shrubs resembled the living cycads in general outer appearance. SPERMATOPHYTA 6i The stem in most forms was thick and short and closely covered with an armor of persistent leaf-bases (Fig. iq). Among these leaf-bases were wedged numerous small Fig. 19. — A fossil cycad, Cycadeoidea marylandica Fontaine (Xi), from the Potomac formation (Comanchean) of Maryland. At the time of fossilization it was about to blossom. Nearly thirty flower buds (/. b) show here between the old leaf-bases. The wonderful preservation of some of the flower buds embedded in these ancient fossilized trunks is seen in Figs 21, 22. branches, each terminating in a fructification. The stem usually bore at top a crown of large cycas-like leaves (Fig. 20). As in general appearance, so likewise in the anatomy of the 62 AN INTRODUCTION TO THE STUDY OF FOSSILS stem, there was a close similarity between these plants and the living cycads. Some of their characters, such as their lateral branching and the hairlike and papery scales profusely covering the leaf-bases recall the cycadofilicales and the ferns. In the structure of their fruiting organs, how- ever, the cycadeoids were peculiar to themselves, and showed an advance over the other orders. They had a true flower since both male and female organs were borne on the same axis and were arranged in the manner typi- cal of the later flowering plants, — the angiosperms. This flower (Fig3. 21, 22) con- sisted of a sheath of hairy overlapping bracts inclosing a circle of leaf-like, pollen- bearing organs analogous to Fig. 20. — Cycadeoidea jenyieyana. Photo- graph ( X 3) of a longitudinal section through a silicified young leaf not yet emerged from the bud. (From Wie- land.) stamens, central to which is a conical axis bearing stalked seeds, the " receptacle " of higher plants. The seeds are often so well preserved in various species that the embryo may be distinguished ; this is dicotyledonous, dif- fering from that of other gymnosperms in occupying nearly the whole seed. This is, however, the only order of fossil plants in which an embryo has been sufficiently well preserved to be studied in detail. In general appearance, therefore, these plants at once suggest the cycads ; in the large, leaf-like stamens and certain features of their pollen sacs they indicate an affinity with the ferns, and in the possession of true flowers they distinctly approach the angiosperms. SPERMATOPHYTA 63 It has seemed evident to students of these analogies that the cycadeoids, as their name implies, are closely related to the cycads, and that both groups sprang separately from certain Paleozoic fernS; the marattiaceous type. Moreover, the structure of their Fig. 21 a. — The unexpanded flower of Cycadeoidea dacotensis Macbride, from the terrestrial deposits of Upper Jurassic age in South Dakota. Photograph ( X 2) of a vertical section of a silicified specimen. The lines refer to various sections through the flower pubHshed in Wieland's "Am. Fos. Cycads." p., pinnules: r., receptacle. fructification, the arrangement of its parts into a '' flower," suggests that the cycadeoids represent an intermediate stage in the supposed line of development of the angiosperms from their fern ancestors. 64 AN INTRODUCTION TO THE STUDY OF FOSSILS This order formed the dominant vegetation of the Mesozoic ranging from the Triassic into the Potomac (Comanchean). It was exceedingly abundant during the Jurassic in North Fig. 21 b. — Restoration of flower bud of Fig. 21a, based upon many other examples besides this figure. Nine of the eighteen staminate fronds (Jr.) are shown folded with reduced pinnules (p.) bearing densely packed oval synangia, — pollen sacs (in white). At the center is the pistillate portion of the flower, the elongate conical receptacle (r.) covered externally with short stalked ovules (ov.) separated by scales, br., bracts; ped., pedicle, or stalk, attaching the flower to the stalk. (Both figures from Wieland.) SPERMATOPHVTA 65 America, Europe, India and the Arctic regions. Especially fine representatives of the genus Cycadeoidea (Bennettites) are found in the upper Mesozoic of Maryland, South Dakota, Wyoming and Mexico. The genus Wielandiella from the Upper Triassic (Rhaetic) had slender stems branching dichotomously J 2 J Fig. 22. — The flower-bud of Cycadeoidea colossalis removed from between the old leaf bases which form the heavy "armor" of the trunk of the plant. This is such a flower-bud as that shown at f.b. in Fig. 19. i. Outer features of the cap- sular disk of stamens which incloses the central cone ; bract-husk mostly cut away; diagrammatic. 2. Same as preceding but with a quarter of the bud cut away so as to disclose inner seed cone and structure of the outer disk. 3. Dome of bud drawn in relief down to level of transverse section (T) and then continued below by a median longitudinal section. The disk of stamens (D) divides into ten fronds each of which sends up two prolongations to form the apical dome (T-C) of twenty segments. The ten once decurved tips of the fronds envelop the seed cone (.4). At 5 are the synangia or complex pollen sacs. Compare with Fig. 21. Natural size. (From W'ieland.) and bore its flowers in the forks. Another genus, Williamsonia, is also of varied structure and had a cosmopolitan distribution in the Jura-Cretaceous. To the genera already mentioned 66 AN INTRODUCTION TO THE STUDY OF FOSSILS various cosmopolitan leaf genera of the Mesozoic, as Podozamites, Zamites, etc., are hypothetically attached. Family 2, CycadecE, the existing cycads or sago palms. — Plants with thick, columnar stems, at times attaining a height of thirty to sixty feet. The trunks are covered with an armor of old leaf-bases and bear a crown of large, usually once pinnate leaves, with from one or two apical cones to as many as thirty in one Australian form. The fructifications are in nearly all genera cones, either male or female, the sexes being separate on different plants. In the female plant of the living Cycas, how- ever, the reproductive organs are not compacted into a cone, but consist of simple, leaf-like blades on which are borne the unprotected seeds. This is the simplest arrangement of repro- ductive organs among living seed plants and is reminiscent of ferns. Another primitive character of the cycads is their method of fertilization. In most of the living seed plants the male cells are carried by the pollen tube to the ovule (Fig. 11, E'). In the cycads and ginkgos alone among seed plants the male cells are ciliated and motile, swimming actively to the ovule after the rupture of the pollen tube, as is usually the case in the crypto- gams, — the ferns, mosses and many algae. This motility of the male cell is a survival of the earlier stages of the process of plant evolution when water was an essential medium for the process of fertilization, and of a still earlier stage when the whole plant body was adapted to life in the water. Living cycads are tropical. There are nine genera, of which Cycas, the best known eastern genus, is found in Asia and Australia, and Zamia is the most conspicuous American genus. They existed in the Mesozoic in some number, but so far definite evidence of them remains meager ; it is the abundance of their kindred, the Cycadeoideae, that marks out the Meso- zoic as the " Age of Cycads," or as some name it " The Age of Proangiosperms." The genus Cycas has been found in the Lower Jurassic, though its leaf type goes back much farther. SPERM ATOPHYTA 67 1. Into what two families are the cycads divided? De- scribe each briefly, stating one respect in which they resemble each other ; one in which they differ. What is their geologic range ? 2. Where are cycads living at present ? 3. Why is the motility of the male cell especially interesting ? 4. Among what plants was the first flower evolved ? Did it resemble any modern flowers ? What testimony does it furnish upon the origin of the higher flowering plants ? 5. Sketch Cycadeoidea, labeling bracts, flower buds (if present). What do the bracts represent? Make restoration of entire plant, naming stem, crown of leaves. 6. What was the age of cycads ? Order C, Cordaitales An extinct group of tall, slender trees which had a general distribution throughout the world from the Devonian to the Per- mian, inclusive. It is represented by the genus Cordaites. The trunk rose to a height of thirty to one hundred feet and was sur- mounted by a dense crown of branches bearing narrow sword- like leaves. The leaves were distinguished by their conspicuous parallel veins, and their great size, attaining at times a length of three feet. The general structure of the stem resembles that of the coni- fers except in the very large pith, which suggests rather that of the cycads. Casts of this pith cavity, called Sternbergia, are common fossils. They are cylindrical bodies, one to four inches in diameter, longitudinally ribbed and m.arked by transverse constrictions at short intervals. The pith in the living stem ruptured transversely at intervals, dividing into disks of solid tissue separated by empty spaces. In the casts of this cavity, where there is a later decay of the pith and w^ood, the position of the pith-disks would be represented by transverse constrictions. This appearance may be seen on a lesser scale in the pith of the walnut, hickory and other common trees to-day. The fructifications of Cordaites were small male and female catkins. 68 AN INTRODUCTION TO THE STUDY OF FOSSILS In leaf structure and in certain primitive features of the seeds, Cordaites shows relationship to the Cycadofilicales, in stem and root anatomy it inclines toward the conifers (Fig. 23), while its male catkins resemble those of the Ginkgo. From these and other characters it is evident that the Cordaitales Fig. 23. — Photomicrograph of a radial section of one of the most ancient of known woods, Callixylon {Cordaites) oweni Wieland, from the Upper Devonian Black Shale of Indiana. The preservation of this wood is so perfect that the thin sections may be freely studied at 600 diameters. At the 100 diameters shown here, the bordered pits of the radial surfaces of the wood cells or tracheids are seen to have a radially grouped arrangement ; this radial grouping is rare in the I'aleozoic. (After Wieland.) were a highly generalized group of seed-fern afifinity near the base of all the later gymnosperm lines, originating probably in SPERMATOPHYTA 69 the Silurian. Among living gymnosperms, the ginkgos are their closest kin. The Cordaitales are confined to the Paleozoic and seem to have furnished the predominant members of the gymnosperm forests during the Devonian, and especially later during the Carbonif- erous. Cordaites, named in honor of the early paleobotanist, Corda, is the best known genus. In the Upper Devonian black shale of Indiana are trunks two feet in diameter and twenty feet long, indicating trees probably one hundred to one hundred and fifty feet high (Fig. 23). In Pennsylvanian shales in New Brunswdck the leaves are packed in layers like those of modern forests. 1. Describe the appearance of Cordaites. 2. How were casts of its pith cavity formed ? What are they called ? 3. Discuss its relationships and probable evolution. 4. Describe a forest of Carboniferous time as you think it must have appeared. Order D, Ginkgoales An isolated order of gymnosperms, represented at present by only one genus and one species, Ginkgo hiloba, — the maiden- hair tree, but with the long and varied ancient history that such isolation in the existing flora always indicates. The ginkgo is a tree which in general appearance and in the anatomy of the stem closely resembles the conifers. The leaves, however, are fan-like in outline like the large leaflets of the maidenhair fern, and are shed each year. A primitive character which it possesses along with the cycads, and which is reminiscent of a fern ancestry, is the motility of the male cells in fertilization, already mentioned (p. 66). The ginkgo tree has long been cultivated by the Chinese and Japanese, especially in the temple grounds ; now a common cultivated tree, it is not surely known wild in any part of the 70 AN INTRODUCTION TO THE STUDY OF FOSSILS world, though it may possibly be native to western China. It is the last member of a race that is seen by the fossil records to have spread over all the world. This race, the Ginkgoales, was especially numerous and widespread in the Jurassic and was still abundant in Cretaceous time. Leaves and flowers of representatives of this order are found in rocks of these ages in Europe, northern Siberia, Greenland, Spitzbergen, China, Turkestan, Australia, South Africa and the Pacific Coast of America. In at least the earlier part of the Tertiary, the ginkgo flourished in Alaska, Greenland, and the northern part of Great Britain. Because of its great antiquity and isolated position it has been called a " living fossil." It is supposed to have arisen from the group of the Cordaitales. 1. Describe the ginkgo tree. What is its common name and from what derived ? 2. What is the geologic range of this order ? 3. Discuss the present and former geographic distribution of the ginkgo tree. Can you account for this difference? Order E, Coniferales This order includes the conspicuous gymnosperm vegetation of the north temperate regions, made up of trees and shrubs, mostly evergreen, usually with rigid, needle- or scale-like leaves and with male and female cones. The conifers were probably derived from the Cordaitales of the Paleozoic, retaining fewer primitive characters than the Ginkgoales, but derived from the same source. Living conifers are represented by forty genera and three hundred and fifty species. They are divided into two families : (i) Taxacece, the yews. — With fleshy seeds and exposed ovules. Comparatively modern, with no record below the Comanchean, they already during this period formed an im- portant element in the Potomac flora of eastern North America. SPERMATOPHYTA 71 (2) PinacecB. — With dry seeds and ovules covered by scales. These include four tribes : — (a) Araucarice. — A group that is now mainly restricted to a small region of the southern hemisphere — Norfolk Island, Brazil, southwestern Argentina and Chili, but widely distrib- uted during the Mesozoic, being abundant in the Jurassic rocks of Great Britain, Spitzbergen, South Africa, Australia, India, the eastern United States, and in the Antarctic regions. A comparison of the former and the present distribution of such a genus is of vivid interest as indicating former geographic connections which are now severed. From the association of fragments of petrified araucarian wood with the jet at Whitby, England, it may be supposed that \ / -< > Fig. 24. — Transverse section ( X 60) through an annual ring of the Tertiary conifer, Sequoia magnifica Knowlton. sp., cells added during spring or wet season when an abundance of moisture caused rapid growth, hence large cells; su., cells added during summer or dry season ; the cells here are small. The change is gradual from the moist spring to the succeeding dry season, but the next spring's growth begins suddenly, hence here is a very sharp change in size of cells. These more or less sudden changes produce the annual ring, merely a contrast in size of cells, con- trasting periods of slow and rapid growth. (From Knowlton.) some of the jet, at least, consists of the fossilized remains of the wood of Araucaria. {b) Abietcc. — The group of the more common evergreens, — • 72 AN INTRODUCnON TO THE STUDY OF FOSSILS » o V o ^ ^ -^ o Fig. 25. — An ideal section through the fossil forests of Amethyst Mountain, in the Yellowstone National Park. There occur in this region 2000 feet of volcanic material in layers alternating with at least fifteen successive forests, indicating thus fifteen volcanic outbursts separated by at least sufl&cient time to allow the growth of forest trees with a diameter of two to ten feet. (From Holmes.) SPERMATOPHYTA 73 pines, cedars, hemlocks, etc. Recorded from the time of the Comanchean. (c) TaxodicE. — Includes (i) Voltzia from the Upper Permian and Triassic. To this tribe likewise belongs (2) Sequoia (Figs. 24, 25). The genus Sequoia is now represented only by two species, — S. sempervirens, the redwood, and S. gigan- tea, the big tree, — living in restricted areas in California and southern Oregon. These trees are unique in the world in their Fig. 26, A. — Sketch map showing the known distribution of the bald cypress (Taxodium). Tertiary distribution shaded; Pleistocene occurrences north of its present limits, in dots; present distribution black. (From Berry.) size, age, and scarcity. The trunk often attains a height of over three hundred feet and a diameter of over thirty feet. Like Araucaria, Ginkgo, etc.. Sequoia, as at present represented, is merely the lonely survivor of a once widely distributed group. Though not known conclusively from the Jurassic, its twigs, cones, and seeds are abundant in the Comanchean of North America from Virginia-Texas-California, north to Greenland, 74 AN INTRODUCTION TO THE STUDY OF FOSSILS in Spitzbergen and Europe from Russia to Portugal ; it continued in abundance and with wide distribution during the Cretaceous and Tertiary, but disappeared during the cold climate of the Pleistocene, except in the California-Oregon region. Sequoia langsdorfii, the direct ancestor of the redwood, was very wide- spread in the great circumpolar conifer forests of Upper Cretaceous time ; while S. magnifica, so abun- dant in the Tertiary of the Yellow- stone National Park, was almost identical with the living redwood. (3) The genus Taxodium (Fig. 26), consisting of the bald cypress, char- acteristic of hard or sandy bottom swamps, and of a Mexican species, is now confined solely to the southern Atlantic and Gulf Coastal plain ; but in early Tertiary time this genus was as figure 26, A shows, universal north of the tropic of Cancer. Such a map indicates the tremendous changes in plant distri- bution brought on by the advent of glacial conditions in the north polar area, while the recent description of the fossil flora of Graham Land (Upper Jurassic) by Halle shows like changes on a gigantic scale in Antarctica. {<£) CupressecE. — Including the juniper, arbor vitae, etc. Known doubtfully from the Jurassic. Fig. 26, B. — A twig of Taxodium distichum miocen- icum Heer ( X 2), from the Tertian- of Utah. (From Lesquereux.) 1. Name three living conifers with which you are acquainted. 2. What is the geologic range of this order? 3. Into what two families is it divided? 4. What is jet? 5. Discuss Sequoia, noting its appearance, present habitat, and former distribution. SPERMATOPHYTA 75 6. How did the climate of the Tertiary differ from that of the Pleistocene and the present ? What was the chief cause of this difference ? Give examples among plants that show that this climatic change took place. Order F, Gnetales This group of small trees or shrubs consists of three living genera, including P^j^hedra of the desert regions of both hemi- spheres. They differ from other gymnosperms and show some- what angiospermous tendencies in certain structural characters of the wood and in some flow^er-like features of the reproductive organs. Fossil record of the order would have high interest but so far has not been forthcoming. 1. What are the Gnetales? 2. What fossil record have they? SUBDIVISION B, AXGIOSPERM.^ As the mammals represent the culmination of the much branched animal line of ascent, so the angiosperms contain the plants of highest rank. This group, the latest to come upon the earth, comprises over half of all known living species of plants. It is the angiosperms which clothe most of the earth with vegetation ; in every climate and at almost all altitudes they nearly always compete successfully with all other vegetal types. They not only cover much of the earth with forests and grasses, flowering herbs and shrubs, but many species (e.g. water-lily, duckweed) have invaded the fresh-water realm of the algcC with wonderful success. Though very few angiosperms, as the eel-grass (Zostera), have tried to dispute with algae a habitat in the sea, they are the only group to have invaded the sea at all, for the gymnosperms, ferns and mosses have no representatives there. The members of the Angiospermae are commonly known as 76 AN INTRODUCTION TO THE STUDY OF FOSSILS the Flowering Plants (Fig. 27). The typical flower is com- posed of (i) a covering, the perianth, which may consist of an outer bud-covering portion, the calyx, and an inner colored portion, the corolla. The entire perianth may be brightly colored or uncolored. Within the perianth are (2) the male Fig. 27. — Fossil flowers, because of their delicacy, are rarely preserved. A, Carpolithes macrophyllns, from the Miocene shales of Florissant, Colorado. (From Cockerell.) a, entire flower with its four large calyx lobes; b, detail of venation; c, fruit. B, restoration of flower of Combretanthites eocenica, from the Eocene of Tennessee. X 4. (From Berry.) organs, — the stamens bearing the pollen, which are the male cells of fertilization. The stamens are arranged in one or more circles ; at their center is (3) the female organ, the pistil, the outer portion of which, the stigma, receives the pollen while the inner portion, the closed ovary, contains the ovules which after fertilization by the pollen become seeds. The method of fertilization is somewhat complicated. Each dust-like pollen grain is a single cell with a single nucleus at its center. When this pollen grain is lodged, through the agency of the wind or an insect, against the stigma, the usually sugary solution there holds it and causes it to grow. By this time the single nucleus will have divided into two or three, one of which, SPERM ATOPHYTA 77 the tube cell, piercing the stigma, grows down its stalk and pene- trates an ovule, permitting the passage thither of the other two cells (Fig. II, E'). By this time the nucleus of the ovule has also divided several times, forming several cells ; to one of these cells one of the two male cells is attracted, and there results a fusion of the two cells into one ; this fusion is fertilization. Immediately this new cell, nourished by the other cells, grows rapidly into a minute embryo. This embryo consists of a stem with seedling leaves (cotyledons) at one end, and a root at the other. In this state, the seed, it ceases growing and may remain dormant for years. As animals prepare food material — the yolk — for the growing embryo, so also do plants ; in the grasses and palms this nourishment lies in the seed outside the cotyledons, in the bean and walnut within the cotyledons them- selves. It is thus seen that the pollen grain and ovule always develop into distinct plants of a few cells each. These few cells form the sexual or gametophyte stage of the angiosperms, corresponding to the entire liverwort and moss plant and to the prothallus of ferns. The union of two cells, one from each of these plants, produces the embryo which under favorable conditions will develop into the adult plant, — the asexual, or sporophyte stage; it, like the fern-plant or the little capsule of the moss, produces spores called here the pollen and ovules. Both classes of the angiosperms made their first appearance, so far as known, in the Upper Comanchean. Here appeared such modern dicotyledonous genera as the poplar, willow, laurel and fig, as well as primitive representatives of such monocoty- ledonous families as the pondweed and the sedge. This early flora is best known from the Upper Potomac formation (Patap- sco) of Virginia and from strata of corresponding age in Portu- gal. Later upon the Cretaceous lands flourished very lux- uriantly many of our best known living plants, — the oak, walnut, beech, birch, holly and ivy of the dicotyledons, the lily and palm of the monocotyledons. The rapid rise of the angio- 78 AN INTRODUCTION TO THE STUDY OF FOSSILS sperms, — • the true flowering vegetation, — was probably due to the pari passu development of flower-loving insects, the bees and wasps (Hymenoptera) and the butterflies and moths (Lepidop- tera) ; these families first appeared in the Jurassic, the period immediately preceding the one which apparently saw the begin- ning of the angiosperms. Derivation of name. — Angiospermae > Greek angeion, a vessel + sperma, seed, because the seed is inclosed in a pro- tecting ovary, e.g. the core of an apple, the pit of a cherry, the chaff of grass. In the gymnosperms the pollen can reach the ovules directly. The Angiospermae are divided into the classes : — a. Monocotyledones. b. Dicotyledones. Class i, ^Ionocotyledones These plants are usually distinguished by the following char- acters : the plant begins with a single leaflet or cotyledon (whence the name mono-cotyledon) ; the leaves are parallel- veined ; the stem is cylindrical with the vascular bundles scat- tered, a cross section accordingly not showing concentric growth lines ; the roots are fibrous ; the parts of the flowers in threes. This class includes to-day members of vast economic impor- tance to man. The grasses, especially their fruit, the grains, have become an absolute necessity to him in the temperate zones, just as the plantain, banana, and various palms (e.g. date, coco and sago palms) are now an essential to his existence within the tropics. Representatives of the class are first known from the Upper Comanchean of eastern North America and Portugal in such lowly forms as the pondweed and sedge ; the lily and palm, however, soon appeared in the Cretaceous, while not until rather late in the Tertiary did true grasses make their appearance. The paleontologic record of the palms goes back to the mid- Cretaceous (Fig. 28). It is probable that they occurred SPERMATOPHYTA yg rather extensively from this time on ; they were apparently abundant in North America, both on the coastal plain and in the formations of the continental interior. Fig. 28. — Transverse section of the New Jersey Upper Cretaceous palm, Palmoxylon anchorus Stevens. This is an example of the often marvelous perfection of pres- ervation of cell structure in fossilized plants. Portion of a large root ( X 130) ; p., phloem, thin-walled cells, through which most of the organic substances manufactured by the leaves pass down to the roots; .v., xylem, thick-walled woody cells through which the crude materials absorbed from the soil pass up to the stem and leaves; /., an internal vessel surrounded by sclerenchyma fibers, — very thick-walled, strengthening cells. (After Stevens.) Class 2, Dicotyledones The dicotyledons usually possess the following characters, — the plants begin with two seedling leaves, the cotyledons (whence the name di-cotyledons) ; the leaves are usually netted- veined. The stem is usually thicker below than above, with the vascular bundles arranged to form a cylinder inclosing a pith center ; as growth proceeds new cylinders are formed, and 8o AN INTRODUCTION TO THE STUDY OF FOSSILS since the vascular bundles formed in spring have thinner walls than those formed in late summer and fall the annual growth becomes visible as a concentric ring. A taproot is usually present ; the parts of flowers are in fours or fives. The dicotyledons are new generally regarded as more primitive than the monocotyledons and as their probable ancestor. (i) One of the most primitive of the dicotyledons is the American tulip tree, Liriodendron tulipifera, a beautiful forest type, of eastern North America, reaching a diameter of four to twelve feet, and a height of sixty to one hundred and ninety feet. The closely related species, L. chinensis, occurs in eastern Asia. These are the sole survivors of the genus Liriodendron which had formerly a far wider distribution. Appearing first in the Cretaceous in great variety and number of species, it flourished during this period in North America from Wyoming to New Jersey and in Greenland. In Tertiary time it still ex- tended its range over Iceland and Eurasia ; but the cold climates of the Pleistocene forced the last remnants of Liriodendron southward in Europe and finally cut them off on the shores of the Mediterranean Sea, which, with the Alps, acted as a trans- verse barrier to the farther retreat of this and many other types. Thus is explained the paucity of dicotyledons in Europe as compared with North America and eastern Asia, where retreat southward during the ice age was not thus cut off by high moun- tains or transverse shores. This late restriction of distribution is also seen in Engelhardtia (Fig. 29). (2) Sassafras, like Liriodendron, is also a ditypic genus now restricted to S. officinalis, confined to eastern North America, and a closely related Chinese form. Like Liriodendron, it is the last representative of a large group which flourished at least throughout North America and Europe since the Comanchean, but could survive the cold Pleistocene climate only in North America and eastern Asia. It is known first from the Coman- chean of Virginia, Greenland and Portugal, later from the SPERMATOPHYTA 8l Cretaceous of North America (occurring from the Rockies to New Jersey), Greenland and Europe, and it continued to have a cosmopolitan range throughout the Tertiary ; a late Pleisto- cene species from France and ••■' I \ Italy is almost identical with the living form. (3) The poplar (Populus) is known to have lived during Comanchean time in Virginia and Greenland, throughout North America and Greenland Fig. 29. — A, a fossil relative of the walnut family, Engelhardtia {Oreomunnea) mississipplensis Berry, from the Eocene of Mississippi (X h). B, sketch map showing the existing distribution of Engelhardtia (vertical lining) and fossil occurrences (stars). There is here an indication of movement southward as the northern regions became colder, and of the obliteration of this tropical genus from Europe, where southward migration during the glacial period was prevented by the transverse shores of the Mediterranean Sea. (From Berry.) during the Cretaceous, and in Europe, North America and Arctic lands in the Tertiary. 82 AN INTRODUCTION TO THE STUDY OF FOSSILS 1. What is the especial feature that characterizes the angio- sperms ? What is the difference, indicated by the derivation of the words, between angiosperms and gymnosperms ? 2. Describe a typical flower. 3. Outline the method of fertilization. 4. What is the sporophyte stage of an angiosperm ? What the gametophyte ? How does their relative importance among angiosperms compare with it among the mosses ? Among the ferns ? 5. In what geologic age did angiosperms appear ? 6. How are angiosperms divided? 7. Name three features which distinguish a monocotyledon from a dicotyledon. 8. Discuss one example of the former class, giving its geo- graphic and geologic range. 9. Discuss one example of the dicotyledons, giving geographic and geologic range. 1. Name the divisions into which plants are classified, giving the basis of this classification. How does the increase in com- plexity of organization correspond to the order of appearance in geologic time ? 2. Outline the changes in the relation of sporophyte to gametophyte stages from the thallophytes to the spermato- phytes. 3. In what mineralogical state do the majority of fossil plants occur ? Outline the process which changes the living tissue of the plant to this condition. ANIMALS The lines into which life branches do not possess the same power to evolve ; along the animal pathway the three main branches are those of the mollusks, arthropods and vertebrates. In very ancient times each of these phyla had partly at least followed the example of the plants in encasing themselves in a hard external skeleton through which stimuli could with greater difficulty penetrate, and because of which freedom of move- ment was greatly curtailed. Before this condition had become universal, however, branches developed from each, which, an- ticipating historic warfare in this respect, gradually eliminated this protecting but cumbersome armor and developed instead a higher type of nervous system and more responsive muscles. These more progressive branches terminate at present in the squids and devil-fish (Dibranchiata) of the mollusks, the insects of the arthropods and the mammals of the vertebrates. These three .phyla pursued the same pathway through the Protozoa, Coelenterata and possibly also through the worms. From the protozoons to the chordates, as in the human social life, the advance of life is measured by sub-division of labor. In the Protozoa the single cell composing the entire animal performs all the functions which in the Chordata are accomplished by the millions of cells working through hundreds of organs. Natu- rally the work is better done by the latter than by the former. Upon this division of labor as well as upon the varying form of the organs through which the w^ork is performed, the Animal Kingdom is divided into twelve great groups or phyla. PHYLUM I, PROTOZOA The Protozoa are simple, one-celled, aquatic animals consist- ing of protoplasm, usually microscopic in size, with or without 83 84 AN INTRODUCTION TO THE STUDY OF FOSSILS hard parts, and without differentiated tissue or organs. The hard parts, secreted within or upon the surface of the proto- plasm, consist of chitin in some of the Sarcodina, of cellulose in the Dinofiagellata, of calcium carbonate in the Foraminifera, and of silica in the Radiolaria. Protozoa are the most abundant aquatic animals. Two extremes in size among living Protozoa are the organism causing yellow fever, supposed to be a protozoon but so minute that it has never been seen, and Porospora gigantea, a parasite on the intestine of lobsters, which is two-thirds of an inch in length. The same species may vary much in size " due solely to the lack of food in the one case." A living species of Dilep- tus varied from a proportional length of 80 when normal to 10 when starved (13). Derivation of name. — Protozoa > Greek protos, first, + zoon, animal ; in this phylum occur the first or lowest animals. The Protozoa are divided into the following four classes, of which only the Sarcodina and possibly the Mastigophora have fossil representatives : — Page A. Sarcodina , S8 B. Mastigophora 94 C. Sporozoa 95 D. Infusoria 95 Type of phylum. Amoeba proteus (living) (Fig. 30). This is a microscopic mass of jelly-like protoplasm, about .2 mm. in diameter with a clear, usually thin, outer layer and a granular inner portion, the granules being mostly proteid and fat particles. Within this granular portion is a darker, rounded body, the nucleus, and a rounded, pulsating, clear space, the contractile vacuole. It secretes no skeleton, and is free-moving and abundant at the bottom of fresh water pools and ponds among decaying vegetation. It is irregular and variable in outline, continually altering its shape by slowly pushing out and withdrawing PROTOZOA 85 various parts of its body ; these temporary finger-like processes are called pseudopodia. Movement takes place by the gradual streaming of the entire substance of the amoeba into the pro- jections from one side, and is thus practically a flowing process, " the upper surface " (in A mceba verrucosa) ''continually pass- ing forward and rolling under at the anterior end so as to form the lower surface" (15). Its food consists of those entire minute animals or plants, or those organic particles with which the pseudopods, or main body portion have come into contact. The amoeba pursues such prey as long as it is in con- tact with it, rolling it ahead in its attempts to catch it, then sending out pseudopodia on each side to surround it. Fi- nally if the prey has not escaped the amoeba succeeds in sur- rounding it with its side pseu- dopodia and sends out from its upper surface a thin film of protoplasm over it, thus com- pletely engulfing it. This food is pressed into the soft sub- stance and passes gradually into the interior. Digestion. — With the food-victim a certain amount of water is taken in by the amoeba ; this water with the victim forms a '' gastric vacuole " or an improvised stomach, surrounded on all sides by a wall of living protoplasm. From this protoplasm there soon begins to form an acid secretion, probably hydro- chloric acid, which thus gradually changes the chemical nature of the water of the gastric vacuole and kills the prey which it incloses ; with the first changes in chemical nature of the sur- rounding water the prey begins to struggle and ceases its efforts to escape only when killed by the secretion. It is probable that the product of the digestive action of this acid is the formation Fig. 30. — The fresh-water protozoon, Amceba proteus. It is now moving in the direction of the arrow. «., nu- cleus; C.V., contractile vacuole; p., pseudopodia. Very much enlarged. 86 AN INTRODUCTION TO THE STUDY OF FOSSILS of soluble peptones similar to the products of proteid digestion in the higher animals. This is followed by a digestive ferment like trypsin, acting in an alkaline medium. The manufacture of the acid secretion is intimately con- nected with the chromatin material of the nucleus, for digestion does not take place when the nucleus is absent. '' Protozoa evidently have the power of secreting different kinds of ferments in response to the stimulus of different kinds of living food particles." Some types of Protozoa can create starch-dissolv- ing ferments or fat-emulsifying ferments, though other species throw the starch grains out of the body with other indigestible parts of the food (13). Assimilation. — '^ The granules that are formed by the break- ing down of the food particles through the digestive process are ultimately distributed by means of the protoplasm which streams to all parts of the protozoon " through the animal's rolling method of progression and by osmosis. " Some are probably converted directly into protoplasm by an assimilative process that is as little understood in these forms as in the Metazoa " (13). Excretion. — The undigested food particles pass outwards into the surrounding water, and are left behind as the amoeba rolls forward. Thus, whatever part of the amoeba's body touches food becomes mouth, whatever portion the food particle enters becomes digestive cavity, and the undigested material may leave from any part of the surface. It is probable that the contractile vacuole is the chief organ of excretion, that by its means the animal rids itself of the waste products of assimilation and metabolism, such as urea and carbon dioxid. Respiration, or the exchange of gaseous waste products for oxygen, takes place through the entire surface of the body, most of the oxygen being obtained in this way, though probably most of the carbon dioxid is thrown off by the contractile vacuole. PROTOZOA 87 There is no trace of a nervous system, though the animal displays many of the reactions to stimuli which higher forms possess. It is sensitive to chemical changes in the water sur- rounding it and to heat, moving away from the chemically changed area and from the source of heat. It moves away likewise from the source of strong light and toward the negative pole when the water containing it is charged with electricity. It avoids mechanical obstacles in the water by reversing the flow of its protoplasm into the opposite direction. Thus me- chanical, chemical and electrical stimuli and variations in heat and light control the direction of movement (15). Reproduction is mainly by simple division. When more food is taken in than is required for maintaining the size un- altered, a constriction appears dividing the entire amoeba, including the nucleus, into two parts, thus producing two cells or two individuals. Each individual amoeba is a single cell, that is, it consists of a mass of protoplasm with an included nucleus. All animals higher than Protozoa, as well as all higher plants, consist of many such cells, usually with some more or less firm protective or strengthening substance. 1. If Amoeba is available it should be examined under a compound microscope, its shape and movements noted. 2. Give size and structure of the animal. Illustrate with sketch. 3. Where does it live? What does it feed upon? 4. How is food procured ? How digested, and waste thrown off? 5. How is the food assimilated ? 6. How does the animal breathe ? Excrete waste matter ? 7. Does Amoeba possess nerves? How does it respond to stimuli ? 8. Describe its reproduction. 9. Where do Protozoa occur? What is meant by calling them one-celled animals ? 10. What classes of Protozoa have been found fossil ? 88 AN INTRODUCTION TO THE STUDY OF FOSSILS CLASS A, SARCODINA Marine or fresh-water Protozoa with a body which alternately protrudes and retracts first one and then another part into finger- like processes, — the pseudopodia. A contractile vacuole is present in some fresh water but not in marine forms. Repro- duction is by binary or by multiple (spore-formation) fission. The members of this class are relatively large, many being visible to the naked eye. Some of the fossil forms especially, as Nummulites and Orbitoides, attain giant proportions for Protozoa. Derivation of name. — Sarcodina > sarcode > Greek sarx (sark-) flesh. Sarcode was the name applied by Dujardin to what is now called protoplasm. The Sarcodina are divided into the two sub-classes, — 1. Rhizopoda. 2. Actinopoda. Sub-class i, Rhizopoda Usually creeping forms with branched pseudopodia (whence the name from Greek rhiza, a root, + pous (pod-) foot). This is subdivided into the orders, — a. Amcebea. — Amoeboid (changeable) forms, usually with- out shells. Unknowm in the fossil state. The genus Amoeba gives the name to the order. b. Xenophyophora. — This includes some deep sea forms with a peculiar internal structure and a skeleton composed of foreign bodies, such as sand grains, sponge spicules, etc. (whence the name from Greek xenophyra, foreign bodies, + pherein, to bear). Unknown in the fossil state. c. Foraminifera. — Skeleton (test) present, composed of cal- cium carbonate, more rarely of sand or of chitin, forming one or more chambers ; this is perforated by one or more openings (whence the name from Latin foramen, a hole, + ferre, to bear). Pseudopodia are long and slender, uniting at intervals. These are typically creeping forms, using their net-like pseudopodia PROTOZOA 89 to capture food, but some, such as Globigerina and some twenty other modern species, have taken to a pelagic existence, that is, they have become planktonic. Reproduction in the Foraminifera is both sexual and asexual. The sexually produced test results from the conjugation of zoo- spores. It has a microspheric first chamber (proloculum) . With increase in size and in number of chambers the nucleus also divides, often resulting in a greater number of nuclei than chambers. In the adult, each nucleus takes some of the proto- plasm and forms a megalospheric first chamber (proloculum) larger than the microspheric ; this develops into an adult test similar to the microspheric test, but smaller. In this adult form there is a single nucleus which moves forward so as to occupy the middle chamber numerically ; this finally divides, each portion taking some of the protoplasm ; a further division results in zoospores, or it may first continue for some generations repro- ducing asexually. The life cycle, consisting of an alternation of generation, is thus completed (14). Most Foraminifera are marine; a few of the simpler forms live in fresh water. They are now found everywhere in all seas (seldom below 2500 fathoms, since by the time such depths are reached the tests are dissolved). They flourish best in waters free from sediment and are hence much less abundant in estuaries and at the mouths of rivers than elsewhere. Foraminifera did not become rock builders until the Missis- sippian period, Fusulina being one of the earliest to form rock- masses. The chalk of the upper Cretaceous of Europe and of North America (Niobrara, Austin and Rotten limestone forma- tions) is largely composed of Foraminifera ; accompanying these are sponge spicules, sea-urchins and shallow-water moUusks, indicating shallow seas for the growth of these ancient forami- niferal — or globigerina — oozes. Foraminifera occur from the Ordovician to the present. Ow- ing to the resemblance of their convoluted chambered shells to those of Nautilus, they were first classed with the Cephalopoda. 90 AN INTRODUCTION TO THE STUDY OF FOSSILS M .si*? «? ^^fe^iS' Fig. 31. Globigerina (Fig 31). Triassic to present. This differs from Amoeba in the possession of a calcareous support, the test. This test is composed of several globular chambers arranged in an irregular spiral (whence the name from Latin globus, a ball, + gcrerc, to carry). It also differs from Amoeba in the length and delicacy of pseudopodia, which unite with each other at intervals. The chambers are somewhat glassy in appearance, and are pierced by numerous microscopic pores The lime-secreting pro- through which, as well as through tozoon, Globigerina aquiiateralis the large opening from the largest Bradv, from the Gulf of Mexico. , i t This 'species is world-wide in its chamber, the pseudopodia are ex- distribution, in both tropical and tended. The protoplasm is per- fectly continuous throughout all the chambers. The food consists mostly of microscopic plants, such as diatoms and algae, more seldom of the minute copepod crustaceans ; these are enveloped and digested by the net-like pseudopodia. Globigerina typically lives floating at the surface of the ocean, spreading out its pseudopodia in all directions around it. At the death of the individuals, the tests fall to the sea bottom, and accumulate in vast layers, forming the globigerina oozes. Although known from the Triassic to the present, it occurs but sparingly in the Mesozoic. subtropical waters. Three views of the same specimen (much en- larged). The greatest mass of protoplasm was extended through the large opening (O). 1. Examine the specimens under the compound microscope (these should include thin sections of chalk, and some globig- erina ooze or sand scraped from such shells as those from the Paris Basin, from sponges or from corals). . 2. Sketch (a) Globigerina, {h) Textularia (Pennsylvanian to present), usually cone-shaped with two rows of alternating, PROTOZOA 91 communicating chambers, (c) Rotalia (Jurassic to present), chambers of test forming a flat spire. For examining the cham- bers use transmitted hght. Label chambers, large and small openings. 3. Did the protoplasm occupy one or more chambers ? 4. What is the food of Globigerina ? How does its manner of capture differ from that in Amoeba ? 5. Describe the reproduction. 6. What is meant by "alternation of generation" ? 7. What is the signilicance of the name Foraminifera ? 8. If Poraminifera occur in all seas, why do they form such masses as chalk and globigerina ooze when the muds and sands accumulated at the same time have so few ? 9. Is chalk of shallow or deep water origin ? Reasons. Fusulina (Fig. 32). Pennsylvanian. Test spindle-shaped (whence the name from Latin fusus, spindle), bilaterally symmetrical; each chamber extending from end to end so that each whorl completely covers the preceding one ; aper- ture in form of a fissure. Exceedingly abundant in the Pennsylvanian limestone of North America, Russia and Asia. Fig. 32. — The protozoan skeleton, Fusulina secalica Say, abundant in the shallow seas covering Kan- sas during a part of the Penn- sylvanian period. A , surface view showing the fissure-like aperture {a-a). B, cross section showing the internal chambers and the aperture (a). Both enlarged; note scale of A . 1. Sketch (a) entire fossil with opening upwards, (b) cross section, showing method of coiling. 2. Comparing with Globigerina, how did the living animal probably procure its food ? Nummulites (Fig. t,;^). Pennsylvanian to present. Test flattened, lens- or coin-shaped (whence the name from Latin nummulus, diminutive of nummus, a coin). Internally there is a spiral series of chambers. Each whorl completely 92 AN INTRODUCTION TO THE STUDY OF FOSSILS incloses the preceding by means of a lateral prolongation of the chambers. The aperture is an inconspicuous slit at the inner margin of the last chamber. In Nummulites the increase in size is mainly on the periphery, in Fusulina it is mainly axial. A large and a small form are usually found associated in the same rock ; these most probably are the large sexually produced test, and the small, asexually produced test of the same species. Nummulites occur from the Penn- sylvanian to the present, but sparsely ^"S'??^ outside the Tertiary. The one .or two %%;itvl/ forms now living, as off the southeast \*»v-/ coast of Asia, are tropical and sub- ^, , , , . tropical. Nummulites attained their Fig. 5S- — The skeleton of a ^ marine protozoon, Nummuii- maximum abundance during the Eo- ^.., from the Eocene of Egypt. ^ making limestone masscs, — A very small specimen en- " ' larged. A, surface view of nummuUtic limestone, up to several the coin-like shell. 5 section thousand feet in thickness, in the parallel to the nat surface. _ ' East Indies, Japan, South Asia, South Europe, North Africa and Central America. The largest species in these rocks attains a diameter of 60 mm. ; the smallest, 2 mm. Associated with these Nummulites are other marine forms, such as mollusks and corals. The great pyramid of Cheops is built of this limestone. 1. Sketch (a) surface view, (h) longitudinal section, {c) trans- verse section. A thin section made from nummulitic limestone will usually give the above sections. 2. How does this differ in its manner of coiling from Fusulina ? 3. What is the significance of the name? 4. When and where did it occur most abundantly ? 5. Account for the large and small forms usually found asso- ciated in the same rock. Orbitoides (Fig 34). Cretaceous to Miocene. General shape of test very similar to that of Nummulites, but the chambers are smaller, much more numerous and com- plicated. PROTOZOA 93 Orbitoides is very abundant in the lower Tertiary. In the Gulf States of North America it makes up in places the entire rock, just as Nummulites does in the Med- iterranean region of Eurasia and Africa. The Vicksburg or Orbitoides limestone of Oligocene age attains a considerable thick- ness in Alabama. 1. Sketch (a) surface view, (b) longitu- dinal section, (c) transverse section. 2. How does this differ from Nummulites? Sub-class 2, Actinopoda Usually floating forms with ray-like, un- branched, rarely changeable pseudopodia provided with an axial thread (whence the name from Greek aktis {aktin-) a ray, + pous {pod) foot). This is subdivided into the orders : a. Heliozoa, commonly called the " sun- animalcules " because of the fine ray-Hke pseudopodia (whence the name from Greek helios, sun, + zoon, animal). These do not possess the chitinous central capsule char- B Fig. 34. — A protozoan calcareous skeleton, Orbitoides, abounding in the Oligocene sea at St. Stephens, Ala- bama. ^ , surf ace view (X i). B, vertical sec- tion along line a. C, section of another specimen much en- larged, m.ch., median chambers ; this row- is much larger than the ones {l.ch.) upon either side ; l.ch., lat- eral chambers. Fig. 35. — Siliceous skeletons of Radiolaria, from the Miocene of Maryland. A, Hexalonche micro- sphcrra Vinassa (X130). B, Cenosphccra porosissima Vinassa ( X 160). (From Martin.) acteristic of the Radiolaria. They are almost confined to fresh water. Unknown in the fossil state. Ex- ample, Actinophrys. b. Radiolaria (Fig. 35). The body is composed of a central mass of protoplasm inclosed in a perfo- rated, chitinous membrane, the central capsule, and is continuous through this with a layer of pro- toplasm outside the membrane; this layer gives off ray-like pseu- 94 AN INTRODUCTION TO THE STUDY OF FOSSILS dopodia (whence the name from Latin radiolus, a little ray). There is usually present, in addition to the central capsule, another skeleton, beautiful and delicate ; this is secreted by the protoplasm, usually without, sometimes extending or originating within the central capsule ; it consists of isolated spicules, bars or latticework made of silica (Fig. 35), or rarely of acanthin, a substance allied to chitin. When the silica is secreted it is throwm down in the protoplasm all at once, apparently at the supersaturation of the protoplasm with silica. The Radiolaria are marine organisms, floating at the surface of the ocean, or even at abyssal depths, and present in all climates. In some deep parts of the Pacific and Indian oceans these shells, falling after the death of the animal, accumulate on the sea-bottom, forming a siliceous deposit, known as " ra- diolarian ooze." The Radiolaria did not become important rock builders until the Tertiary ; before this they occur only in scat- tered siliceous cherts but from nearly all periods. The Bar- bados earth, Miocene in age and covering large areas in the Barbados Islands, resembles very closely the modern radio- larian ooze and is probably a deep-sea deposit. Heliodiscus and Astromma are two genera found here. In the '^ Barbados earth " the siliceous skeletons of radio- larians still retain their originally amorphous condition. Usually these skeletons are dissolved soon after burial in the rocks by percolating waters containing alkali and may be redeposited as chert. The chert nodules of the upper Cretaceous chalk are probably largely due to these skeletons. Radiolaria occur from the pre-Cambrian to the present. CLASS B, MASTIGOPHORA Protozoa with a definite body outline, the body protected in some species by a skeleton of cellulose or chitin, but usually naked. Organs of locomotion and of food-capture in adults are the flagella, — slender threads capable of whip-like lashing move- ments (w^hence the name from Greek mastix, a whip, + pherein, to bear). Euglena is an example. PROTOZOA 95 Fossil representatives of the order Dinoflagellata with a cellulose skeleton are reported from the flint in the European Cretaceous (Blitschli). CLASS C, SPOROZOA Parasitic Protozoa. There are no definite organs of locomo- tion or of food-getting in the adult. Reproduction is typically by the formation of seed-like bodies, — spores (whence the name from Greek spora, seed, + zoon, animal). Each spore contains one or more minute germs, — sporozoites. Unknown in the fossil state. Gregarina and Plasmodium are two of the common genera. Three different species of the latter may cause human malaria. CLASS D, INFUSORIA Protozoa with a definite body outline. The organs of loco- motion and food-capture during all or a part of their active life are cilia, — small vibratile threads, smaller and more nu- merous than flagella. There is a vegetative large macronucleus and a smaller generative micronucleus. (The name was origi- nally applied to all those minute plants and animals that make their appearance in infusions of decaying organic substance, but is now restricted to Protozoa as defined above.) Unknown in the fossil state. Examples are Vorticella, Paramcecium and Stentor. PHYLUM II, PORIFERA (SPONGES) Sponges are organisms consisting of many cells, plant-like in appearance and extremely variable in shape. Sponges grow- ing side by side will frequently fuse into one mass, and almost any fragment of a sponge will grow into a perfect individual. They are fixed, aquatic, and usually colonial animals. Nearly all sponges are marine and are most abundant in the shallow parts of the ocean (Euspongia, Cliona) ; but some with a siliceous skeleton (Euplectella) occur in the abyssal portions. The only sponges inhabiting fresh water are the green sponges (Spongilla, etc.) ; the natural color of these is a light gray, but they are usually colored green through the presence of algae. Typically a simple sponge looks like a hollow, attached vase ; it consists of a cylindric body pierced by many canals which conduct water through the wall into a large central or paragas- tric cavity ; this opens to the exterior by a large opening, the osculum. Water is drawn in through these many small canals and forced out through the large osculum. These canals are of three kinds, {a) the incurrent, leading from the outside into the wall of the sponge, (b) the flagellate or gastral, and (<:) the excurrent, leading into the central cavity. The flagellate canals, — the gastral layer, consist in all sponges of collar-cells ; they are the principal organs for the capture and digestion of food. The paragastric or central cavity may be very deep, often is very shallow, at times it may disappear so that the excurrent canals are upon the surface. Forms with one central cavity and one osculum are regarded as individuals, those with more than one as colonies, but as it is difficult to distinguish between 96 PORIFERA 97 small oscula and large excurrent canals, the distinction of indi- viduals from colonies is likewise difficult. The sponge is not a colony of protozoons, but an individual, for not until an osculum is formed can it feed and reproduce. The skeleton consists of calcareous or siliceous spicules or of horny fibers, all developed in the mesogloea. In the develop- ment of either calcareous or siliceous spicules there is first formed an organic thread at the center of the cell ; around this axial thread the mineral matter is deposited. The calcareous spicules, of almost pure calcium carbonate, are deposited in a crystalline condition, each spicule behaving optically like a single crystal. The siliceous spicules are composed of colloidal silica which is deposited in concentric lamellae alternating with organic lamellae. The spicules of the Hexactinellida, when united, are joined by a secondary deposit of silica, but those of the Tetractinellida and Monactinellida are at times united by spongin, at others the spicules are enveloped in spongin, as in Chalina ; finally in the Ceratospongida the spicules disappear and spongin alone remains, as is seen in the common bath sponge. Sponges are classified according to this skeleton. The Myxospongida, with no skeletal elements, and the Ceratospongida, with skeleton of perishable fibers of spongin, can seldom be preserved as fossils. Practically all fossil sponges, therefore, belong to the orders secreting siliceous or calcareous spicules. In these orders fossils may be preserved in two states. If the skeletal framework is sufficiently firm to hold together after the death of the animal, and consequent disappearance of the soft parts, it may be preserved in its entirety, as for example in Prismodictya and Astylospongia. If, however, this framework is composed of spicules so loosely bound together as to fall apart upon the disappearance of the soft parts, the scattered spicules alone will be preserved, as in Lyssacina, Cliona and Renieria. During fossilization the composition of a sponge skeleton may be greatly modified. In those forms wath siliceous spicules H gS AN INTRODUCTION TO THE STUDY OF FOSSILS the silica is in a colloidal condition ; during fossilization this becomes crystalline, or is dissolved and carried off by percolat- ing waters or is replaced by calcium carbonate or some other substance. Likewise the calcareous spicules are often replaced by silica. Thus originally siliceous spicules may be converted into calcite and calcareous spicules may become silicified. Hence the distinction between siliceous and calcareous sponges in the fossil state depends upon form and not upon chemical composition. When the siliceous spicules are so loosely bound together as to fall apart upon the decomposition of the soft parts of the animal, they will collect in the depositing sediment and where abundant form porous siliceous beds. Usually the spicules have undergone partial solution in sea- water ; this dissolved silica being redeposited as siliceous cement binds the remaining spicules together. Since the spicules are so very small their presence is detected only by an examination of thin sections of the chert under a high power microscope. The silica from such dissolved spicules and from other siliceous organisms is fre- quently redeposited as nodules of flint. The flint nodules in the Cretaceous chalk beds of England and France are notable examples. Sponges are known from the pre-Cambrian to the present. Derivation of name. — Porifera > Latin porus, a pore, + ferre, to bear ; referring to the many minute incurrent canals penetrating the wall of the sponge. The Porifera may be divided into the following sub-classes : Page A. Calcarea 102 B. Non-Calcarea 102 The old sub-class Silicispongiae include the Hexactinellida, TetractineUida and Monactinellida ; while the apparently more genetic sub-class Desmospongiae includes the TetractineUida, Monactinellida, Ceratospongida and Myxospongida. Accord- ing to this latter classification all sponges would be divided into Calcarea, Hexactinellida and Desmospongiae. PORIFERA 99 Type of phylum, Grantia ciliata (living) (Fig. 36). This is a hollow cylinder, somewhat spindle-shaped, about half an inch high by a quarter of an inch wide, attached at base to some solid object. It is dull yellow to gray in color, with a large opening edged with spicul-es at its summit. It is found , lues. Fig. 36. — The common sponge, Grantia ciliata. The protecting and supporting spicules are calcareous. A, longitudinal section (x 10). B, transverse section ( X 250). b., bud; e., eggs; en., endoderm lining the flagellate canals, each armed with a single long cilium ; ex.c, excurrent canals; /., "flesh" of sponge; fl.c, flagellate canals; in.c, incurrent canals; mes., mesoglcea, with scattered nuclei; 0., osculum ; os., ostia, the outer openings of the incurrent canals; o.sp., the very long spicules surrounding the osculum ; p.c, paragastric cavity ; sp., the long spicules surrounding the ostia; sp'., the three-rayed spicules surrounding the flagellate canals; sp.c, paragastric cavity shown in longitudinal section. (After Brooks, relettered.) growing in tide pools from Rhode Island to Greenland and on the northern coasts of Europe. The body wall consists primarily of three cell-layers, ectoderm, endoderm and mesoglcea. It is protected and a firmness given lOO AN INTRODUCTION TO THE STUDY OF FOSSILS to the walls by a network of interlacing calcareous spicules. These are microscopic, spike-like calcareous bodies, with one to four rays. Each spicule is secreted by a single mesogloeal cell, the remains of the cell being at times still distinguishable as a thin investment upon the surface of the full-grown spicule. Food and Digestion. — The entire surface of the sponge is perforated by numerous, minute holes (ostia), through which a current of water enters the incurrent canals (lined with flattened ectodermal cells) ; from here it enters the elongate flagellate canals and passes out into the large central, or paragastric cavity by the short excurrent canals ; these elongate flagellate or gastral canals are lined with endodermal cells, each of which is furnished with a protoplasmic collar from within which projects a thread-like lash, the flagellum ; these cells are very similar to certain Protozoa, — the Choanoflagellata, of the class Mastigophora. These flagella, having a stronger and swifter movement in one direction, moving in some forms ten times a second, cause the currents of water to pass from the outside through the incurrent, flagellate, and excurrent canals into the large central or paragastric cavity and thence out through the large opening, — the osculum, at the summit of the sponge. The excurrent canal is in Grantia very short, a mere opening ; in all the higher sponges, as in Spongilla, it is very long. This current of water carries with it many mi- croscopic animals and plants, and food particles, which the collar-cells capture and ingest by means of the flagella and col- lars ; each cell acts thus as a single protozoon. Wandering amoeba-form cells take part in digestion ; these can move from one part of the sponge to another. Thus digestion usually takes place within individual cells as in the Protozoa. Circulation. — The transference of the digested particles of food from the digestive cells to the rest of the body is largely a process of simple osmosis, — the cells having recently digested food being denser than the others ; it is aided also by the very free wandering of the amceba-form cells and to a less extent by PORIFERA lOl the mesogloea, into which some cells cast fluid or solid substances which are taken up by other cells. All waste, such as undigested material, etc., is carried out through the osculum. Exchange of waste gases for oxygen is also effected by this current of water. Around the outer edges of the incurrent and excurrent canals and the osculum are elongate cells (ectodermal and endodermal) which are contractile and thus represent muscles. These muscle cells effect the closing of these openings. There is probably in all sponges a total absence of special nerve cells, and hence a great lack of coordination in cell move- ments, " thus the flagella of the collar-cells do not beat in uni- son like the cilia of the epithelia in higher animals, but each works independently of the others " (17). Reproduction takes place through the development of the sexual reproductive cells, — spermatozoa and ova ; these develop from the amoeboid wandering cells of the mesogloea, which for this take up their position directly below the flagellate cells. Both ova and spermatozoa are developed in the same sponge individual, though rarely at the same time. The amoeboid cell, to form spermatozoa, divides into many small cells, each of which develops a long tapering tail. The amoeboid cell, to become an ovum, simply becomes round and enlarges, and after a sperm has penetrated it, thus effecting impregnation, the ovum becomes inclosed in a brood-pouch made by the neighboring cells. In its development the ovum, after its impregnation, divides into two cells ; these divide again and again, resulting in a hollow sphere, the blastula. In this shape, the embryo es- capes to the exterior and moves about by means of flagella. Later the layer of cells from one side bends in against the layer of the opposite side, forming a double-w^alled cup, the gastrula. The opening of this gastrula cup, the blastopore, gradually closes, and at this stage of its development the young sponge becomes fixed by the side on which was situated the blastopore ; an open- ing, the osculum, breaks through at the opposite end and the 102 AN INTRODUCTION TO THE STUDY OF FOSSILS incurrent, flagellate, and excurrent canals develop. The osculum thus does not correspond to the gastrula opening, as it does in the Coelenterata, but is a later development opposite it. 1. Examine (a) an entire Grantia, (b) longitudinal and trans- verse sections under the compound microscope. 2. Show by diagram how the animal eats. What does it eat 7 3. How is the food digested ? assimilated ? 4. How is respiration effected ? excretion ? 5. How are the soft parts of the body supported and the animal protected ? 6. Are muscles present ? 7. What is the nervous system like ? 8. Describe the reproduction and the development of an animal from the egg to maturity. 9. If the genus Grantia were to become extinct, what record of its former existence and of its appearance would the rocks preserve ? SUB-CLASS A, CALCAREA Skeleton of calcarous spicules (whence the name from Latin calx, lime). Spongin not present. At present these sponges occur in the shallower portions of the sea bordering the coasts ; the fossil representatives (Middle Paleozoic to the present) lived under similar conditions, judging from the marly or sandy nature of the strata inclosing them. Living examples are Grantia (described on page 99), and Sycon. SUB-CLASS B, NON-CALCAREA Skeleton of siliceous spicules, of spongin fibers, or absent. This sub-class is divided into five orders. Order i, Hexactinellida. — Skeleton of six-rayed siliceous spicules (whence the name from Greek hex, six, + aktis, a ray + Latin diminutive ella). When these spicules are united with each other, it is through the addition of secondary silica, never of spongin. To this order belong most of the fossil sponges. At present they are characteristic of deep water, but the ancient PORIFERA 103 forms, as the character of sediment and associated life forms indicate, lived mostly in comparatively shallow water. They are known as fossils, at least from the Cambrian to the present. Euplectella aspergillum (Venus' flower basket) (Fig. 37, B). Living. A tubular cornucopia-shaped sponge with a transverse, ter- minal sieve-like cap at its summit and an anchoring root-tuft at its base. The skeleton consists of siliceous threads, each of which is probably the greatly elongated ray of one axis of a three- to six-rayed spicule (the other rays being suppressed), cemented in adult life end to end to others by the addition of secondary silica.- This process results in the formation of long, vertical, spiral and circular threads which form a polygonal net- work around the central cavity. There is usually one ostium in each quadrangular interval. The vertical threads terminate in the conical root-tuft which forms the base. Upon the out- side there are ornamental spiral ridges (whence probably the name from Greek eu, well, + plektos, twisted). It grows at considerable depths in the ocean fastened by the penetration of the stiff threads of the root-tuft into the mud or ooze. This species was dredged by the Challenger Expedition from a depth of 95 fathoms, and E. crassistellata from a depth of 2750 fathoms. 1. Sketch side view of entire specimen, labeling cap, root- tuft, ostia. 2. What is the composition of the skeleton? function of the root-tuft ? 3. Give the probable origin of the long threads. 4. Describe the process by which Venus' flower basket could leave a record of itself in the inclosing sediments. Prismodictya (Fig. 37, A). Devonian- Mis sis sip pian. An elongate, slender, gradually expanding, eight-sided prism ; each prism-face reticulated by the spicular threads, which are arranged regularly in larger and smaller quadrate meshes sit- uated one wdthin another. Found as internal molds (16). This sponge was very similar to Venus' flower basket, though I04 AN INTRODUCTION TO THE STUDY OF FOSSILS .-^ A Fig. 37. — Comparison of a fossil and a modern glass sponge. A, internal mold of Prismodictya prismatica Hall; very abundant in the ocean covering New York state during the Upper Devonian time. Natural size. B, the siliceous skeleton of Venus' flower basket, Euplectella, about a foot high, living in the East Indian seas. 0., osculum, the opening of the large central cavity {p.c) now partially filled with mud. At the junction of the principal bands of spicules (sp.b.) were probably tufts of spicules, the bases of which have left their impressions (sp.t.) upon the internal mud mold. Prismodictya was probably attached to some foreign object by a flattened area at o. A modified from Hall and Clarke. PORIFERA 105 without its siliceous cap or anchoring root-tuft. After the decomposition of its soft parts, sediment very readily oozed through the meshes of the skeleton, completely filling it. Upon this sediment were impressed the form of the skeleton and the shape of its quadrate meshes. With the disappearance of the hydro-siliceous skeleton through the destructive agency of alkali-bearing percolating waters, the shape of the mass of sedi- ment within the skeleton remained. Prismodictya belongs to the family Dictyospongidas (Silurian- Mississippian). These, unlike their modern representatives, — Venus' flower basket, lived in comparatively shallow water. Most of the Devonian forms, as Hydnoceras, were anchored in sand or sandy muds by their root-tufts, while in the Mississip- pian the majority were apparently fastened to a solid object, — stone or dead shell, by a more or less broadened base ; this last was probably also the case wdth Prismodictya. Ornamental ridges may also occur {e.g. Clathrospongia and Thysanodictyon) , upon the outer surface as in the modern Euplectella. Prismodictya prismatica is very abundant in the upper Devonian (Chemung) sandstones of the Appalachian region. 1. Sketch side view of entire specimen with a small portion in detail, noting the quadrate meshes. 2. Describe the steps in the formation of this fossil from the death of the animal to its present appearance. 3. How did the living Prismodictya differ from Venus' flower basket ? Order 2, Tetradinellida. — Skeleton of four-rayed siliceous spicules (whence the name from Greek tetra, four, + aktis, ray, + Latin dim. ella). When these spicules are united with each other, it is through the addition of spongin. These are known in the fossil state from the Cambrian to the present. Astylospongia (Fig. 38). Ordovician-Silurian. Spherical, with a shallow depression (osculum) at the sum- mit, and with many pores (incurrent canals) over the entire I06 AN INTRODUCTION TO THE STUDY OF FOSSILS OS. outer surface. The rigid skeleton is probably due to the irreg- ular mesh-like union of the spicules. 1. Sketch entire specimen, labeling osculum, incurrent canals. 2. How would you know this to be a sponge ? Order j, Monactinellida. — Skeleton of one-rayed siliceous spicules (whence the name from Greek monos, one, + aktis, ray, + Latin dim. ella). When these spicules are united with one another it is through the addition of spongin. This order includes the few fresh- water sponges (Spongilla, etc.) and the majority of existing marine sponges ; they inhabit the more moderate depths. They are known from the lower Paleozoic to the present. The boring-sponges (Cliona) are compound forms with many oscula. They secrete pin-shaped siliceous spicules encased in spongin, with which, aided by a power of absorption, they bore passages in dead or living shells for protection, not for food. These sponges and boring worms help to perform the same function in the economy of nature in the sea as fungi and insects do upon land, namely the disintegration of dead organisms. Order 4, Ceratospongida. — Skeleton of horny, spongin fibers (whence the name from Greek ceras, horn, + spongia, sponge). Not definitely known in the fossil state. The common bath sponge (Euspongia) is an abundant living form. The common commercial sponges grow in warm seas, as those of the West Indies and the Mediterranean, from tide level to a depth of 200 feet. When prepared for commerce they are torn from the sea-bottom, exposed on the hot beach to decompose, then washed in water to remove all fleshy parts, leaving the tough, Fig. 38. — The sponge, Astylo- spongia prcemorsa Goldfuss, from the Middle Silurian of Indiana. X 2. Side view showing the osculum {os.) above. (After Hall.) PORIFERA 107 fibrous, chitinous skeleton. The separate individuals of these usually compound sponges are distinguished only by the oscula ; the rest of the body is intimately united with its neighbors. Order 5, Myxospongida. — Skeleton absent (whence the name from Greek myxa, mucus, + spongia, sponge). Unknown in the fossil state. 1. Since a protozoon consists of a single cell and a sponge of many cells, why cannot the latter be considered a colony of the former ? 2. What is the principal advance of the Porifera upon the Protozoa ? 3. What is the characteristic skeletal element in sponges? Give variations in its chemical composition and in its structure, with examples of each. 4. Amongst the different sponges, give stages of the gradual replacement of spicules with spongin. 5. Give the habitat of commercial or bath sponges. How are they prepared for market ? Are they simple or compound ? 6. What function did the various holes in the common bath sponge have when the animal was living ? 7. Why do the boring sponges penetrate shells? 8. From the rocks of what period is the earliest record of sponges ? PHYLUM III, CCELENTERATA The Coelenterata are aquatic, usually marine animals, with a radial (instead of a bilateral) symmetry and with the mouth opening into the digestive cavity (coelenteron) ; this latter usually forms the entire body cavity. The mouth is nearly always surrounded by tentacles, — hollow or solid outgrowths of the body wall. A cross section of the body wall or of a ten- tacle shows it to be composed of three layers, an outer layer of cells (ectoderm), an inner layer of cells (endoderm) and between these two a layer of a rather stiff structureless substance (meso- gloea) inclosing few or no cells. These animals are provided with special offensive weapons, the nettle-cells (nematocysts) . Derivation of name. — Coelenterata > Greek koilos, hollow, + enteron, intestine. The entire cavity within the body walls acts as a digestive cavity (like the stomach and intestine of higher animals). The Coelenterata are divided into the following classes : — Page A. Hydrozoa io8 B. Scyphozoa 121 C. Anthozoa 122 D. Ctenophora 139 CLASS A, HYDROZOA (HYDROIDS AND MEDUS.E) Type of class, Sertularia pumila (living) (Figs. 39, 40, C). This is a colonial form with the individuals, — the polyps, in sessile cone-shaped cups (hydrothecae) arranged in two oppo- site row^s along a stem. The polyp consists essentially of a hollow, sac-like digestive cavity, surrounded at the top by a single circle of tentacles, and in the midst of the tentacles an 108 CCELENTERATA — HYDROZOA 1 09 /J opening, — the mouth. The stems, an inch to an inch and a half long, simple or branched, spring at intervals, usually in clusters, from a creeping and much branching root-stock (hydrorhiza). This species is very abundant off the northeast coasts of North America from New Jersey to the Arctic, also on the northwest coasts of Europe. It occurs in espe- cial profusion be- tween tides at- tached to the rock weed, Fucus. Each polyp is continuous at its base with the central canal ; its entire surface se- cretes a protec- tive layer of chitin composed of superposed lamellae. When mature it largely draws away from this protective covering. There is thus formed a cup out of which the animal can expand to get food, and into which it can withdraw for protection. Its food consists of small, usually microscopic animals and plants, as well as of organic fragments. These it catches with Fig. 39. — A portion of a colony of the hydroid, Sertidaria pumila, from the coast of Massachusetts, cce., coenosarc. — the common flesh uniting; the various individuals of the colony, — through which passes the central canal ; dig., digestive cavity; gth., gonotheca, or cup lodging a reproductive polyp; hth., hydrotheca, or cup lodging a feeding polyp; m., mouth; p., a polyp expanded, in feeding position; />'., a polyp contracted, in protected position; /., tentacles. X 60. no AN INTRODUCTION TO THE STUDY OF FOSSILS its sixteen tentacles and by their aid pushes into its mouth. The tentacles are covered with numerous nettle-cells (nemato- cysts) by means of which any living prey is paralyzed and thus rendered harmless. Through the mouth, the food enters the large, central or digestive cavity, into which is poured a digestive fluid secreted by some of the smaller endoderm cells lining this cavity. The undigested waste is thrown out again through the mouth, while the digested food is taken up by the bordering cells through osmosis, and thus passed to all the cells, each tak- ing what it needs for repair or growth. Respiration is performed by the entire surface of the body, for the covering of the cells of the ectoderm (the surface layer of cells) is so thin that osmotic interchange of the excess carbon dioxid of the animal for the oxygen of the water easily takes place. There are many muscular fibers, especially along the inner edge of the ectoderm, the contraction of which enables the animal to shorten its entire body and thus withdraw into its protective cup. Accompanying these muscles are large, much- branched nerve cells in contact with one another for the regu- lation of their action. Reproduction is both sexual, through the development of spermatozoa and ova, and asexual, by budding. Some of the digested food passes through the base of the polyp into the central canal, and up this to the growing tip, where new buds for the formation of new polyps occur ; some passes into polyps which are completely inclosed in urn-shaped cups (gonothecae) ; these latter, — the reproductive polyps, cannot procure their own food, but give rise to spermatozoa or ova, the union of tv/o of which produce a new colony. Reproductive polyps are present only during the breeding season, from May to September. Within the gonotheca develop (by budding) usually only minute jelly-fish, — the medusae ; these breaking loose from the parent swim about freely and develop spermatozoa and ova, the CCELENTERATA — HYDROZOA III union of which gives rise to the sessile colony, — the hydroid. This alternation of generation may be represented thus : — 1ST Generation 2D Generation 3D Generation Colony feeding polyps reproductive polyps — medusae males Greek hydor, water, + zoon, ani- mal. The Hydrozoa are subdivided into the following orders : — Page T. Graptolithida 113 Leptolinae 120 Trachylinae 121 Hydrocorallinae 121 Siphonophora 121 There is a growing tendency to make the Graptolithida a sub-class of the Hydrozoa, or even to make them a distinct class of the Coelenterata. They differ from the Hydrozoa in the presence of (i) the sicula and (2) the virgula; also in (3) the bilateral symmetry of the thecae, seen even in the sicula. Since the apex of the sicula, i.e. the embryo-sheath, lacks growth lines it probably possessed the radial symmetry characteristic of the typical Hydrozoa. This embryo-sheath is quite similar, except in composition, to the primary cup of Tabulate corals, as is likewise the alternate budding of new cups (thecae). On the other hand very many graptolites, Uke Diplograptus, were similar to the existing hydrozoan order Siphonophora in the presence of a float (pneumatocyst), and especially like the living Sertularia of the hydrozoan order Leptolinae in ar- rangement of thecae, presence of generative cysts (gonangia) and composition of protective covering. Order i, Graptolithida (Graptolites) Type of order, Diplograptus foliaceus (fossil) (Fig. 40). This species is like the true hydrozoon, Sertularia, in being colonial. It consists of two crowded rows of cups (hydrothecae) like saw teeth, arranged in opposite series along a stalk to which they are broadly but obliquely fastened. Each cup, a sub- prismatic tube longer than wide, represents as in Sertularia one individual polyp ; in it were lodged the soft parts and into it the entire polyp could withdraw for protection. At its base I 114 AN INTRODUCTION TO THE STUDY OF FOSSILS it was connected by means of a tube with the central canal running the length of the stalk. Unlike Sertularia, however, it was not attached to the sea-bottom in shallow water, but floated freely at its surface suspended from a float-like disk (Fig. 40,/.), somewhat like forms included with the hydrozoan order Siphonophora. Fig. 40. — Diplograptus foliaceus Murchison, from the Utica (Ordovician) shale of New York. A, a compound colony of graptolites. Natural size. B, a young graptolite just emerged from the reproductive bladder (r.). Natural size. C, the living hydrozoon, Sertularia pumila ( X 2), for comparison of external forms, fl., the supporting float-like disk ; r., reproductive bladders in three of which are young graptolites (siculse, s.) ; th., thread supporting the colonies (c, c' .) ; c, side view of colony showing the two rows of cups ; c' ., front view showing the width of the cups. A, B, slightly modified from Ruedemann. As in Sertularia, the protective covering was of chitin, but its partial decomposition, due to its great age, aided probably by the heat engendered by pressure of the overlying sediments, CCELENTERATA — HYDROZOA T15 has resulted in drivdng off most of the hydrogen, oxygen, and nitrogen, thus leaving as fossil only a film composed mostly of carbon. It was very probably similar to Sertularia in the character of its food, its digestive, excretory and nervous systems, and in its assimilation and respiration. Its reproduction was likewise both sexual and asexual, and it seems to have lacked the jelly-fish stage. The union of a sper- matozoon and ovum gave rise to the first polyp which secreted the earlier protective cup, called the sicula. From this by bud- ding developed the colony (rhabdosome) . In the genus Diplograptus (Ordovician-Silurian) the cups (hydrothecse) are arranged in two row^s along the stem (whence the name from Greek diploos, double). In a side view, the vir- gula shows as a raised ridge running through the middle of the colony, while each cup has a thick outer edge owing to the com- pression of its entire width. D. joliaceus is abundant in the Utica (Ordovician) shales of eastern North America and in the Ordovician of Europe. 1. Sketch a portion of the colony, enlarging it three times. Label cup, virgula, sicula (if present). 2. In life what part of the animal was probably visible outside the cup when feeding ? 3. Give in tabular form resemblances to and differences from Sertularia. 4. What is the chemical composition of the fossil ? What produced this change from its composition when living ? General Survey of Order Graptolithida Extinct, colonial Hydrozoa, fixed to some object upon the sea- bottom, or floating upon the surface attached to drifting sea- weed or to a pneumatocyst of their own manufacture. They secreted a protecting and supporting skeleton of chitin, with the separate individuals lodged in pits upon, or cups along the margin of, the chitinous stalks. Il6 AN INTRODUCTION TO THE STUDY OF FOSSILS These extinct Hydrozoa are known only from their colonial phase, the presence of the jelly-fish phase not yet having been demonstrated. Some forms, at least, as Diplograptus, devel- oped direct, without the alternate generation ; here generative C3^sts formed on the colony, in which developed the siculae (embryonic graptolites) ; the rupture of these cysts scattered the siculae ; each surviving sicula grew into a new colony. Habitat. — Graptolites, with the exception of some of those belonging to the sub-order Dendroidea, lived suspended. That they did not live fastened to the sea-bottom is shown by the fact that their remains are always confined to one bedding plane, never passing vertically from one bed to another. They are always spread flat as though they had fallen with the entombing sediment. While they are found in all kinds of sediment, in- cluding limestones, they are most numerous in very fine-grained, carbonaceous shales. The carbon of the shales was probably de- rived from floating marine plants, not from the abundant grapto- lite remains, for seldom, if ever, do decomposed rhabdosomes pass into the surrounding shales. Since few land plants were prob- ably in existence during Ordovician times, — the climax of grap- tolite development, — it is likely that the carbon is due to the par- tial decay of marine plants. Many fragments of seaweed occur in such typical graptoHte beds as the Utica shale of the Ordo- vician of the Appalachian region. Suspended from these plants were representatives of the Axonolipa division of the Graptoloidea, while floating among them were Axonophora colonies supported by their pneumatocysts. The latter prob- ably sank during periods of roughened seas, as some of them had developed ridges which might have subserved such a directive function. A roughening of the water surface would cause a rain of the broken, fragile colonies upon the sediment beneath. This method of growth accounts likewise for the wide distribution of so very many of the species. That even the Graptoloidea sub-order was derived from forms which grew upright upon the sea-bottom as did many of the Dendroidea CCELENTERATA — HYDROZOA 1 1 7 is suggested by the reversion of direction of the cups in a col- ony, the embryonic cup or sicula growing in a direction oppo- site to the rest of the cups (20). Graptolites were abundant during the upper Cambrian, the Ordovician and the Silurian, while a few stragglers continued to exist into the Mississippian. Derivation. — Graptolithida > Greek graptos, written, + lithos, stone. The resemblance of these fossils, especially those of the sub-order Graptoloidea, to the ancient writings on stone suggested not only the name of the order but also the latter part (graptus) of most of the generic names of graptolites. The graptolites (Order Graptolithida) are sub-divided as follows: Sub-order a, Dendroidea. — Colony (rhabdosome) branching irregularly in a funnel or fan-like manner. Cups (hydrothecae) usually pits upon the branches. Probably most of the Dendroidea, especially the heavier and more shrub-like forms, were sessile in an upright position, attached to some object at the sea-bottom ; this would likewise account for their local distribution. Some have adhesive threads (hydrorhizae) , like Sertularia and other modern sessile hydroids. Many of the species of Dictyonema, on the other hand, have a very wide distribution, and, at least in their younger stages, floated about attached to a supporting disk. The name is from the tree-like (Greek dendron, a tree) method of growth of the colony. Dictyonema (Fig. 41). Cambrian-Mis sis sip plan. Colony (rhabdosome), a rapidly expanding fan or cone with cups upon the inside. The slender branches are united at short intervals, producing a net-like appearance (w^hence the name from the Greek dictyon, net, + nema, thread). When young, the rhabdosome was suspended from a long, thin thread attached to a chitinous disk; later (at least at times), it was sessile by rootlets. D. flabelliforme is common in the earliest Ordovician rocks of eastern North America and western Europe, Il8 AN INTRODUCTION TO THE STUDY OF FOSSILS I. Sketch the fossil; if the entire colony is not preserved, dot in its probable shape and size. 2. Where upon the colony did K the individual animals live ? 3. What probable difference between the habitat of the young and of the adult ? Reasons. Sub-order b, Graptoloidea. — Colony (rhabdosome) simple, or if branched it is not tree-like. Cups (hydrothecae) usually dis- tinctly marked and projecting. The Graptoloidea lived sus- pended, floating. This sub-order embraces two divisions : — (i) Axonolipa. Virgula ab- ^'S--- u'^'^r f ''^T.'"^ ■'^''^f 'S'T sent. Representatives of this Lichwald, from the lowest Ordo- ... vician of New Brunswick, showing division were suspended from cups (r) and roots (r ). Natural geaweeds. Named from the size. (After Matthew.) Greek axon, axis, -f- lipein, to lack, referring to the absence of the virgula. Phyllograptus (Fig. 42). Ordovician. Colony consisting of four short, broad, leaf-like (whence the name from Greek phyllon, leaf) branches grown together, each pair back to back, in such a way as to form a cross in section. Hydrothecae upon the outer edge of each branch. 1. Sketch entire colony, labeling the cups. 2. Make an ideal cross section through the colony. (2) Axonophora. Colony with a median axis, or strengthen- ing rod of chitin, called the virgula, running its entire length. The division Axonolipa is replaced from the mid-Ordovician onward by the Axonophora, i.e. those with an axis (virgula). This axis of chitin is brittle, which probably accounts for the CCELENTERATA — HYDROZOA 119 ca. fragmentary condition of most of these species. The virgula extends through the entire colony (rhabdosome), even penetrat- ing the sicula. Prob- ably all of the Ax- onophora were at- tached to a float of their own secretion. Examples are Diplo- graptus (p. lis), Cli- macograptus and Monograptus. Named from the presence of the vir- gula, from the Greek axon^ axis, + pherein, to bear. Climacograptus (Fig. 43). Ordovician- Silurian. Hydrotheca? sharply curved below, the upper edge or aper- ture more or less hori- zontal ; hence they are widely separated. The colony thus pre- sents a ladder-like appearance (whence the name from the Fig. 42. — Phyllograpius angustijolius Hall, from the Ordovician of New York. A, entire colony ( X 4), showing the earliest cup, the sicula {s.); the opening of the latter is between the two spines. B, trans- verse section through the colony (X 6); ca., common canal with its four longitudinal septa; th., the in- dividual cups (theca;). C, P. ilk if alius Hall (X 8), showing the openings of five cups, in each of which was lodged the soft body of a single individual. (All from Ruedemann ; A and B after Holm.) Greek climax, a lad- der). The straight outer margins of the hydrothecae are parallel to the axis of the colony. C. typicalis is very abundant in the Utica (Ordovician) shales of New York State. I20 AN INTRODUCTION TO THE STUDY OF FOSSILS 1. Sketch a portion of a colony, indicat- ing a hydrotheca and its aperture. 2. What is the chemical composition of the fossil at present ? When living ? 3. How do you account for the great abundance and the fragmentary condition of these colonies, as for example in the Utica shale ? Fig. 43. — The grap- tolite, Climacograp- tus typkalis Hall (X 7), from the Utica shale of New York. Only the end of the colony bearing the sicula is.) is here shown. (From Ruedemann.) Monograptus (Fig. 44). Silurian. Cups (hydrothecae) arranged in one row along the straight or curved stem (whence the name from the Greek monos, one). The virgula can be seen as a ridge extending the length of the colony | opposite the cups. M. clin- tonensis is an abundant and well-preserved species in the Silurian (Clinton) shales of New York State. 1. Sketch portion of a colony, enlarging it three times. Label a hydrotheca and its aperture, the virgula, the position of the central canal. 2. Sketch the probable appearance of the soft body of a polyp with tentacles expanded. 3. Briefly describe the probable digestive system of Monograptus. 4. How was the hydrotheca formed ? 5. What use did this cup subserve ? 6. What is the significance of the name Monograptus ? 7. Give reasons for placing this under the Coelenterata rather than under the Porifera. Order 2, LeptolincB. — Hydrozoa which dur- ing one generation are fixed to some foreign object, as seaweed, and grow by budding, very much like a plant. These bud off por- 'A Fig. 44. — The grap- tolite, Monograptus clintonensis Hall, from the Clinton formation (Middle Silurian) of New York. Side views. A , natural size (from Hall) ; B, an en- largement of six cups. (From Ruedemann.) CCELENTERATA — JELLY-FISH 1 2 1 tions of themselves, which usually become free-swimming jelly-fish (medusae) ; these in turn produce eggs and sperm, the union of which gives rise again to a fixed generation. Known from the Mesozoic to the present. Living examples are Obelia and Sertularia (see p. 108). Order j, TrachylincB. — No fixed generation discovered ; all are free-swimming medusae. No fossils known. Order 4, Hydrocorallince. — Colonial Hydrozoa, the common base of the colony secreting a massive calcareous support. Known from the pre-Cambrian to the present. Millepora is a living genus, while the species of Stromatopora were very abun- dant and important limestone builders in the Paleozoic. Order 5, SiphonopJwra. — Colonial, pelagic Hydrozoa, with remarkable diversity of form among the various individuals in a colony. They are often supported by a float of their own manufacture. Not known in the fossil state. Example, Portuguese man-of-war (Physalia). CLASS B, SCYPHOZOA (JELLY-FISH) Large, free-swimming, umbrella-shaped jelly-fish (medusae). The margin of the umbrella is usually lobed, bearing tentacles, while the mouth occupies the position of the umbrella's handle. They develop directly from the egg or by the alternation of a sessile stage ; in the latter case they multiply by transverse fission. They swim by rhythmically opening and closing their um- brella-like bodies. Their food consists of small fish, crustaceans, and even of each other. None live longer than a year. The Scyphozoa are known to have existed from the Cambrian (Fig. 45) to the present. They are entirely without hard parts and consist of about 99 per cent water, so that only under ex- ceptional conditions have they left a record of their presence. At times in very fine-grained muds, as in the lithographic slates of Bavaria (of Jurassic age) impressions of their soft bodies are preserved, or even imprints of their tentacles trailing over the yielding mud. At other times the lobed digestive cavity has 122 AN INTRODUCTION TO THE STUDY OF FOSSILS become filled with fine sand or mud ; this mud or sand filling becoming covered by other mud before the soft jelly-fish body A B Fig. 45. — A fossil jelly-fish, Brooksella alternata Walcott, from the Middle Cambrian of Coosa Valley, Alabama. A, top view showing the nine lobes and a trace of the furrow in the ring about the central disk ; B, under view of same specimen. The lobes are shown, as also are what appear to be oval arms (.r) for carrying food to the central stomach. A central depression {%') may represent the position of the mouth. Natural size. (After Walcott.) has become disintegrated preserves the outline of its contain- ing cavity (Fig. 45). Derivation. — Scyphozoa > Greek scyphos, cup, + zoon, ani- mal, referring probably to the inverted cup-hke appearance of the swimming jelly-fish. CLASS C, ANTHOZOA (CORALS) Type of class, Astrangia dance (living) (Fig. 46). This is a colonial form, with the individuals, — the polpys,— in sessile, star-like cups encrusting stones, dead shells, etc. Living and active it looks much like a tuft of white, translucent moss ; after death and the decomposition of the flesh nothing is seen but a calcium carbonate mass (one-half to three inches in diameter) of star-like cups (coralHtes), each with a diameter of three to five millimeters. It lives in shallow seas off the coast of North America from CCELENTERATA — CORALS 123 Florida to Cape Cod ; it does not occur in the colder water north of the Cape. Each polyp, glassy white and translucent in appearance, con- sists of a barrel-shaped body, averaging 3 mm. wide by 9 mm. Fig. 46. — The common coral, Astrangia dance (x 12), from Long Island Sound, showing a polyp in feeding position upon the calcareous, cuplike base {cu.), also (at left) the coral portion of a bud without its secreting polyp, col., the spongy pseudo-columella ; cu., the cuplike calcareous base secreted by the polyp; cu' ., part of the cup sectioned transversely ; dig., digestive cavity, — the entire interior of the barrel-shaped body; me., mesenteries; mo., mouth; ne., clusters of nettle- cells, by means of the poison in which the prey is paralyzed; a\, oesophagus; s., septa (which alternate with the mesenteries) ; /., tentacles (one is partly dissected to show that its hollow interior is continuous with the large digestive cavity of the polyp). high when fully expanded, with a circle of 18 to 24 long, tapering tentacles surrounding the top. At the center of the top and slightly raised is the oval mouth ; this leads through a short 124 AN INTRODUCTION TO THE STUDY OF FOSSILS oesophagus into the large digestive cavity. The digestive cavity constitutes the entire interior of the body, but is partly divided into compartments by radial partitions {mesenteries, Fig. 46, me.) ; each intermesenteric compartment is continuous with a hollow tentacle. The polyp preys upon marine animals, — small crustaceans, worms, etc. These it catches with its tentacles. Each tentacle ends in a white knob and is speckled all over with white warts, each one of which is a cluster of nettle-cells (nematocysts). When one of these cells is touched it sends out a long barbed, thread-like tube, through which poison is forced. This multi- tude of nettle-cells, piercing the prey, paralyze it. The tentacles then push this food into the mouth, through which it enters the digestive cavity. The white cords (mesenteric filaments) edging the mesenteries are crowded with nettle-cells ; these cords, wrapping themselves about the prey, complete the killing, while the many gland cells covering the cords pour out a digestive fluid. After the digestion of the food, the waste is thrown out through the mouth ; the digested portion mingled with the sea water is forced by the contractions of the body through the radial compartments and into the tentacles, the various cells taking what they need for growth and repair. The entire body acts thus as a huge blood-vessel, and since the digestive cavity connects freely through the mouth with the water of the ocean, the " blood " consists of sea water mingled with nutritive por- tions of food. Respiration is performed mainly by the tentacles ; these being thin and containing the body fluid or blood, permit a free inter- change of the excess waste carbon dioxid, etc., of the body for the free oxygen in the sea water. Well-developed muscles are present. There is a sphincter muscle surrounding the body at the top which draws in the ten- tacles and closes the mouth much as a string may close a bag by gathering it together. Muscular layers line the mesenteries on CCELENTERATA — CORALS 1 2 5 each side, and it is through their expansion and contraction, thus admitting and expelling water, that the animal is able to expand and contract. When the animal is disturbed these muscles contract, the tentacles are rolled inward and the entire body becomes a small dome-like mass. There are no sense organs present, excepting specialized tac- tile cells. There are many nerves present in both ectoderm and endoderm which regulate the complexity of the animal's move- ments. Astrangia reproduces by development of spermatozoa and ova. The sexes are distinct. The reproductive elements form by the division of some of the endoderm cells of the mesenteries near the lower end of the body. The product of the union of an ovum and spermatozoon develops rapidly into an ovoid, hollow body, the planula (blastula stage). This elongate body has two layers of cells, an inner (endoderm) and an outer ciliated layer (ectoderm). After swimming about for a time by means of its cilia, the planula settles down to the bottom of the water and becomes attached. At the free end an inbending of the wall occurs, forming mouth and oesophagus and finally piercing the inner cavity (gastric cavity). Secretion of lime. — After the larva sinks down from its free-swimming condition and rests upon some object, certain ectoderm cells (calicoblasts) of the base of the animal begin to secrete a calcareous liquid directly exterior to themselves, and from this is inorganically crystallized the calcium car- bonate (18) (Fig. 47). According to some students the '' cal- careous deposit is laid down within the individual calicoblasts of the ectoderm. At the same time new ectodermal cells are formed next the mesogloea, and these which are undergoing calcification become loose external layers of partly calcareous, partly organic tissue." Ogilvie. This deposit, developed between the base of the animal and the rock or other foreign object to which it is attached, grad- ually forms a calcium carbonate base (called the basal plate) outlining the size and shape of the ba?e of the soft parts of the animal. At the same time the soft basal portion between the mesenteries bends upward, permitting a greater deposit of Hme Fig. 47. — Vertical section through the edge of a very young stage of the coral, Astroides calicularis, which has fixed itself to a piece of cork (r.). Very much en- larged. The deposits of lime {b., ep.) are apparently thrown down outside the ectoderm {ec.) but through the agency of these cells, b., basal plate ; ec, ectoderm ; en., endoderm ; ep., epitheca ; mg., mesogloea ; m., mesentery ; s., septum, developed by upward bending of wall of animal between the mesenteries (m.—m.) upon the basal plate (b.). (Redrawn from Lankester's Zoology, after Von Koch.) here ; since the mesenteries radiate from the center to the edge of the soft body portion so these ridges (septa) of calcium car- bonate radiate likewise. These septal ridges grow higher and higher, resulting finally in the thin septa, over each of which are folded the three layers — ectoderm, mesogloea and endoderm. The upper edges of the septa are conspicuously toothed, giving them a saw-like appearance. The septa are seen to alter- nate with the mesenteries but are external to the polyp, i.e. each septum corresponds to a radial inpushing of the base and lower sides of the polyp. The outer portion of the barrel-shaped body of the animal early bends upw^ard faster than the inner portion ; it thus results that the non-porous deposit of lime thrown down by the ectoderm takes on a cup-like appearance, called the calyx, with the septa extending from the edge of the cup down to its center. Later the longest septa, expanding, unite with one another to form a spongy, central mass, the pseudo-columella . As the animal grows in circumference and adds new mesen- CCtLEI^TERATA — CORALS 127 teries, and new tentacles, so the coral base enlarges in circum- ference and new septa develop between the older ones, — six in the first set, six in the second, twelve in the third. The ani- mal thus impresses its growth stages from youth to maturity upon its coral secretion, and accordingly we would look towards the narrower end of the coral for the record of its youth. The basal portion of the polyp grows a very short distance from the edge of the cup out over the shell or stone upon which it is fastened; from this basal expansion bud up new polyps, while from their basal expansions or from that uniting them with their parent or each other, arise other buds. All these finally develop into polyps capable of catching and digesting their own food ; but until then, they grow through the nourishment contributed by all the other polyps, for the digestive cavities of all the colony are continuous with one another through these basal expansions, — the common flesh, or ccenosarc. 1. Examine Astrangia, noting the tentacles, mouth, oesoph- agus, mesenteries and their relation to the septa, digestive cavity, nettle-cells. 2. Examine the sea anemone: {a) an entire specimen; {h) an individual sectioned vertically through the mouth. Note tentacles, mouth, oesophagus, mesenteries. 3. What is the habitat of Astrangia ? 4. Of what does its food consist ? How does it procure it ? 5. What keeps the prey from struggling after being sw^al- lowed, and thus injuring the soft body of its captor? 6. Briefly describe the digestion of the food, excretion of the waste and the method by which the nourishment reaches all parts of the body. 7. How does Astrangia breathe? 8. What muscles are present ? Their use ? 9. What is the function of the nerves ? 10. What sense organs does it possess ? 11. Describe the development of Astrangia from the egg to adulthood, noting quite fully the development of the hard parts. 12. What record of this development is present in the coral secretion of an adult ? 13. How does a single polyp become a colony ? 128 AN INTRODUCTION TO THE STUDY OF FOSSILS General Survey of Class Anthozoa Usually sessile polyps differing from Hydrozoa in the posses- sion of a short oesophagus, differentiated from the digestive cavity, and in the division of the body chamber into radiating compartments by means of the mesenteries. Some Anthozoa, as the sea anemone, are without hard parts, but in most forms a skeleton of lime or chitin is secreted by the ectoderm, more rarely by the mesogloea. The simplest form of coral skeleton is that composed of microscopic spicules of lime carbonate of different shapes, developed in great quantities in the mesogloea and remaining detached, as in Alcyonium (" dead men's fingers "). In some forms the spicules are firmly cemented together, thus forming tubes {" organ-pipe coral," — Tubipora) or a branching axis {" precious red coral," — Corallium). In most corals there are no spicules present but a calcareous skeleton is secreted by the outer surface of the ectoderm of the lower part of the polyp. This entire skeleton is called the corallum; when consisting of one individual it is called simple ; when of many, it is termed compound. In the latter case each individual is termed a corallite. In a simple coral, or a corallite, the outer wall {theca) bounds the radiating vertical plates {septa). The depression in the broad end of the coral, called the calyx, was occupied by the base of the polyp and into this it could partly withdraw for protection. In many corals the theca is surrounded by another calcareous layer with ring-like wrinkles, the epitheca; this was secreted by the exter- nal surface of the ectoderm at the base of the polyp. In some forms the partial or complete absence of one of the principal septa caused the formation of a groove or fossida ; it has been suggested that the mesenteries bounding this produced most of the reproductive elements. For the formation of the septa and basal plate see page 126. Projecting upward from the base at the center of the coral is often a little column, the columella; this is secreted by the center of the base of the polyp ; the ecto- CCELENTERATA — CORALS 1 29 derm bends upward just as in the formation of septa, except that it is domed up instead of being ridged up. In the interior of a coral there are usually present besides the septa, tabulae and dissepiments. TabidcB are the transverse partitions extending across the entire space within a coral from wall to wall, secreted by the ectoderm of the base of the polyp like successive basal plates. As the sides of the theca in some species grow higher the polyp cannot occupy the entire interior and hence draws itself upwards, and wherever it rests for a time a tabula is built beneath it. These periods of quiescence may follow the expend- iture of energy at times of reproduction, either sexual or asexual. Dissepiments are the horizontal or oblique plates connecting adjoining septa, formed in a manner similar to tabulae, except that the base of the polyp is withdrawn in sections, not as a dis- tinct whole, nor at such regular intervals. The nettle-cells (nematocysts) contain barbed threads (some about one-fortieth of an inch long) which can pierce by their sudden unrolling a man's calloused foot ; millions occur on the tentacles. Each one is used but once, but new ones are con- tinually being formed. The polyp can reproduce lost parts and a small piece of the base can reproduce the w^hole animal. Reproduction is sexual or asexual. In sexual reproduction the reproductive elements are formed in the endoderm of the mesenteries ; there is no medusa stage. The new animal resulting from this method of reproduction is a single individual. In asexual reproduction the process of budding or of division forms from this single individual a colony of various shapes and often of great size. In the Alcyonaria buds are always formed on tubular outgrowths of the polyps, the solenia, never directly from the polyps {e.g. Tubipora, Syringopora) . In the Zoantharia buds arise directly from the polvp or from the coenosarc. Except for a few forms, this sub-class (Zoantharia) is divided into the perforate and the imperforate orders. In the perforate corals (as Madrepora) the spongy tissue (coenenchyme) is perforated by many canals I30 AN INTRODUCTION TO THE STUDY OF FOSSILS permanently connecting the digestive cavities of all the polyps of the colony ; the coenenchyme is deposited both around these canals and by the superficial coenosarc. In the imperforate corals (as Astrangia) there are a few canals between the surface of the coenenchyme and the coenosarc, not penetrating the coenenchyme; these connect the polyps over the edge of the calices, not directly through the cups. The coenosarc is nour- ished by these canals and secretes the coenenchyme. In the Zoantharia, asexual reproduction takes place also by equal or unequal division, that is, the polyp divides into two or more individuals, each taking a portion of the mouth and some of the tentacles, mesenteries, etc. This division usually takes place by the sides of the mouth growing inward, thus gradually constricting the original mouth. There thus result two mouths in place of one, each surrounded by its own circle of tentacles. Usually the digestive cavity also divides completely so that in each separate polyp the mesenteries and consequently the septa radiate in all directions from a separate center. The incomplete division is illustrated by the " brain-coral " (Meandrina) ; here the mouth divides completely but not the digestive cavity and consequently not the calyx ; a repetition of such division gives rise to the long, calcareous furrows, characteristic of Meandrina, each surmounted by many polyp mouths. Distribution takes place mainly in the larval stage when the animal is free-swimming. All forms are marine. They occur from sea-level to a depth of three and a fourth miles, and therefore at all temperatures. The deep-sea corals are solitary forms. Compound corals are very abundant on coral-reefs. The condition for the reef-building corals is that the tempera- ture be not lower than 68° F., the water usually not deeper than 150 feet, and that there be but little sediment in the water. In the formation of coral-reefs corals enter to a much less degree than was formerly supposed ; in at least many reefs lime- secreting plants are the chief agent. (See p. 2>^.) Anthozoa are known from the Cambrian to the present. CGELENTERATA — CORALS 13 1 Derivation of name. — Anthozoa > Greek anthos, flower, + zoon, animal ; in reference to the flower-like appearance of the expanded polyp, especially of the more brilliantly colored tropi- cal species, the tentacles corresponding to the petals, and the region about the mouth to the disk. The Anthozoa are subdivided into the following sub-classes and super-orders : — Page 1. Zoantharia 131 a. Tetracoralla (Tetraseptata) 131 b. Hexacoralla (Hexaseptata) 133 2. Alcyonaria 135 a. Octocoralla (Octoseptata) 135 b. Tabulata (Aseptata) 136 Sub-class i, Zoantharia Tentacles usually hollow and simple, never pinnate ; they are four to six, or more than eight in number, with a usually equal number of mesenteries and septa. Skeleton present or absent ; when present it is developed by the ectoderm and m.ay be horny or calca- reous, but is never in the form of scattered spicules. Super-order a, Tetracoralla Simple or composite corals with septa in quadrants (whence the name from Greek tetra-, four). Corallum calcareous. Entirely extinct, known from the Ordovi- cian to the Permian. Microcyclas (Fig. 48). Devonian. Simple, disk-shaped (whence the name from Greek mikros, small, -f cyclos, circle). It consists merely of a calcareous plate with ridge-like septa and a fossula. f^*^''^vvr^: -:j^^i^•> ^v•:\^^;:^^ Fig. 48. — A simple coral, Microcyclas discus Meek and Worthen, from the Hamilton CMiddle De- vonian) of Illinois. Jos., fossula; sep., septum. Natural size. (Redrawn from Meek and Wor- then.) 132 AN INTRODUCTION TO THE STUDY OF FOSSILS 1. Sketch specimen, top view, noting septa, fossula. 2. How was the calcareous plate secreted ? the septa ? 3. What is possibly the origin of the fossula ? Heliophyllum (Figs. 49, 2). Devonian. Coral usually a single cup, not compound ; septa numerous, slightly twisted near center of coral and thickened on their sides by conspicuous vertical ridges (carinae). (Name from Greek helios, sun, + phyl- lon, leaf (coral) because of the septa radiating conspicuously like the rays of the sun.) H. halli from the Hamilton forma- tion of eastern North America is one of the most abundant American species ; in this as in all true Heliophyllums, carinae are lacking for some distance from the apex of the cup, and then appear only gradually. It thus in its individual development passes through a stage in which in this respect it is similar to Streptelasma, a Tetracorolla coral ranging from the Ordovician to the Devonian. Fig. 4g. — The coral Helio- phyllum halli E. and H. from the Hamilton (Middle Devonian) formation of New York. This limestone mass was deposited by a single individual, as can be told by the septa (s.) radiat- ing from a center. The flesh of the animal rested upon this mass and within the central, cuplike cavity ; it covered only the upper portion. Natural size. (From Hall.) I . Sketch {a) view of entire specimen, showing both side and top, (b) horizon- tal section near top, (c) horizontal sec- tion near tip. Note septa, carinae, dissepiments. 2. How were the septa formed? the carinae ? the dissepi- ments ? 3. What does the section i c suggest as to the ancestry of Heliophyllum ? Columnaria (Fig. 50). Ordovician to Devonian. This is a closely compound coral with prism-shaped corallites (whence the name from Latin columnarius, formed of columns). CCELENTERATA — CORALS 133 The corallites are thick-walled with well-developed tabulae. The polyp occupied only the space above the last-formed tabula. A B Fig. 50. — Columnaria alveolata Goldfusis, an abundant coral in the Ordovician seas which covered most of the present area of the North American continent. A, transverse section ( X 2I) through eleven entire individuals; B, longitudinal section of three of the individuals, s., septa ; /., tabulae. (From Lambe.) It is much like Favosites, but without mural pores and with septa well developed or present as vertical ridges. 1. Sketch a group of three or four corallites, showing both sides and top ; grind one corallite down until it shows the tabulae. Label corallites, septa, tabulae. 2. Did a single or several polyps secrete the corallites sketched ? Reasons. 3. How did the polyp form the septa ? the tabulae ? 4. Outline a polyp upon your above sketch. Super -order b, Hexacoralla Simple or composite corals with septa in cycles of six or mul- tiples of six (whence the name from Greek hex, six). Corallum calcareous, horny or fleshy. Here are included the reef-build- ing and deep-sea corals of to-day. The Hexacoralla are abun- dant from the Triassic to the present. The few Paleozoic (Silurian-Permian) forms referred to the Hexacoralla may belong to the Tetracoralla. The living sea anemones belong here likewise. These pos- 134 AN INTRODUCTION TO THE STUDY OF FOSSILS sess no hard skeleton, either in adult state or at any time during their development. They are not known in the fossil state. The brown sea anemone {Metri- dium marginatum) extends from New Jersey to Labrador ; a large specimen measures 3 inches wide by 4 inches high. The orange-streaked anemone {Sagartia lucice), especially abundant from New Jersey to Massachusetts, is marked by twelve longi- tudinal orange streaks. It is about one- quarter inch wide by three-eighths inch high. Madrepora (Fig. 51) Tertiary to present. Coral compound, branching, with small, tube-shaped corallites embedded in abun- dant vesicular coenenchyme. Each cor- allite has from six to twelve septa, which are sometimes imperfectly developed. The corallites terminating each branch are the largest. (Name from Latin mater, mother, + porus, a pore, — i.e. a light, friable stone.) Fig. 51. — The ter- minal portion of a branch of a madre- pore coral. The in- dividual polyp at the tip was the largest. cor., corallites, each occupied during the life of the colony by a separate individ- ual polyp. ( X i|.) 1. Sketch five or six corallites at the tip of a branch, enlarging two times. Label corallites, septa, coenenchyme. 2. How was the coenenchyme produced ? 3. Account for the branching of Madrepora. 4. Outline a single polyp in place upon the above sketch. 5. How does Madrepora aid in the formation of coral reefs ? CCELENTERATA — CORALS 135 Sub-class 2. Alcyonaria Tentacles hollow, pinnate, always eight in number as are likewise the mesenteries. A calcareous skeleton is apparently present in all ; it is usually composed of separate spicules which develop in the ectoderm but often pass into the mesogloea. These forms may have in addition a horny skeleton. They occur from the Ordovician to the present. Super-order a, Octocoralla Usually composite corals ; skeleton calcareous, or horny, or apparently absent (name from Greek octo, eight, in allusion to the eight tentacles). Ordovician to present. Tubipora. Living. This red coral is com.posed of parallel tubes, — the corallites (whence the name from Latin tubus, a tube, + porus, a pore). During the life of the colony each corallite lodges a polyp. The polyps are connected with one another by horizontal platforms which branch out from the level of the tabulae and from which new polyps arise by budding. The skeleton is formed by the union of the spicules scattered throughout the mesogloea. 1. Sketch (a) top view, {b) side view. Label coraUites, platform, solenia tubes. 2 . How do new corallites arise in the colony ? 3. What are the solenia ? Gorgonia. Living. Compound coral, tree-like, but branching in one plane, and all branches united to their tips by cross branches. The up- bending of the ectoderm of the base forms a branched horny axis extending throughout the colony. The calcareous spicules present in the mesogloea form a coating upon this axis in the dried specimen (whence the name from Latin Gorgonia, Gorgon-like, in allusion to its hardening in the air, just as the Gorgon, or 136 AN INTRODUCTION TO THE STUDY OF FOSSILS Medusa, turned all beholders to stone). During the life of the colony a polyp occupied the position of each minute prominence. 1. Sketch (a) entire colony in outline, (b) a small portion enlarged four times. Note position occupied during life by an individual polyp. 2. How was the horny axis produced? the calcareous coat- ing? 3. What in general is the food of Gorgonia ? Super-order b, Tabulata Composite corals ; walls of corallites, thick, separate. Septa poorly developed or absent. No dissepiments present. Tabulae numerous (whence the name from Latin tabulatiis, furnished with tabulcB, — tables). These occur mostly in the Paleozoic, a few only in the Mesozoic. Aulopora (Fig. 52). Ordovician to Mississippi an. Coral very loosely compound ; all corallites tube-like (whence the name from Greek aulos, pipe, + poros, a pore). Corallites attached to a foreign object by nearly their whole length. Colony produced by submarginal budding. Fig. 52. — Aulopora re pens Knorr and Walch. Nat- ural size. A branching coral growing upon a brachiopod shell, from the Jennings formation (Upper Devonian) of Maryland, cor., coral- lites. (From Clarke and Swartz.) I. Sketch colony, notmg corallites. 2. Outline a polyp in place upon sketch. 3. How did the colony increase in size? Favosites (Fig. 53). Ordovician to Mississippian. Coral closely compound, with the corallites in contact but with separate walls. Corallites prism-shaped (whence the common name '' honey-comb coral " from Latin favtis, honeycomb). Walls perforated by equidistant pores believed to represent CCELENTERATA — CORALS 137 attempts at budding. Septa usually wanting ; tabulae numer- ous and conspicuous. rf^l^ -c //.'! mts mmm^M A B Fig. 5S- — The compound "Honey-comb coral," Fawsites favosus Goldfuss, abundant in the seas covering the eastern portion of North America during the Niagara (Middle Silurian) time. A, top view of colony ; B, side \iew of a colony ; upper portion, showing the exterior with the pores and the vertical striations; the lower portion is a section showing the granular tabulae, c, corallite, — the space occupied by a single individual polyp; c'., corallite with a convex tabula at the surface, margined by the characteristic pits; po., pores (probably unsuccessful attempts of the individuals to bud new individuals) ; tab., tabulae. Natural size. (From Hall.) 1. Sketch a group of five or six corallites, (a) top view, {b) side view of two. Label corallites, tabulae, mural pores 2. How did the colony increase in size? 3. What may the mural pores indicate ? 4. How were the tabulae formed ? 5. What is the significance of the name ? 6. Was the living animal able to move ? Halysites (Fig. 54). Ordovician to Silurian. Coral compound, composed of long, laterally compressed coraUites, and covered by a peritheca. Septa absent or repre- sented by spines; tabulae numerous. Between each pair of 138 AN INTRODUCTION TO THE STUDY OF FOSSILS corallites is a small tube. Budding occurs only from one side, and the young corallites remain in contact with the parent by Fig. 54. — ■ The chain-coral, Halysites catenularia (Linne) from the Niagara (Middle Silurian) of New Jersey. A, top view of a portion of a colony, natural size; B, longitudinal section ( X 5) showing two individuals {cor.) with their slightly con- cave tabulae (/.), and the small connecting tubes {con.) with their very convex tabulae. C, transverse section through the same showing the septa-like spines {sp.) and within the small connecting tubes a section of the highly arched tabulae (/.). (After Weller.) a constricted edge, thus forming chains, in which each corallite is a link (whence the common name, " chain-coral," from Greek Italy sis, chain). 1. Sketch an inch square portion of colony, (a) top view, (b) side view. For side view polish corallites to show tabulae. Label corallites, tabulae. 2. How did the colony increase in size ? 3. Account for the chain formation. 4. What is the significance of the name ? 5. Did each individual animal possess a separate digestive system or did it share a common one with others ? CGELENTERATA — CTENOPHOR A 1 3 9 CLASS D, CTENOPHORA (COMB- JELLIES) Pelagic individuals with no sessile or colonial stage. Tenta- cles when present are usually two in number. Movement is by the large cilia which are fused into comb-like structures ; these are arranged in 8 meridian-like rows or swimming plates. Not known in the fossil state. Example : Cestus (Venus' girdle). Derivation of name. — Ctenophora > Greek kteis, a comb, + phoros, bearing, from the fusion of the large cilia to form comb-like swimming structures. 1. In what respects are the Coelenterates an advance upon the sponges ? 2. Define the four classes into which the Coelenterata are divided, with a living and a fossil (where possible) example of each. 3. Since the large jelly-fish, the Scyphozoa, consist of about 99 per cent water, how have fossil records of them been made ? 4. Distinguish Hydrozoa from Anthozoa, in (a) the soft body, (b) the hard skeleton. PHYLUM IV, PLATYHELMINTHES (FLAT-WORMS) The old phylum Vermes (Latin vermis, a worm) was a com- prehensive group of no exact classificatory value, including soft, invertebrate animals, many bearing a general appearance to the common earthworm. This is divided into four phyla, — Platyhelminthes (flat-worms), Nemathelminthes (round-worms), Trochelminthes (wheel-worms) and Annulata (ring-worms). Body unsegmented, usually flattened from above downward. Digestive canal without an anus, the waste being carried off by the excretory system. No blood vascular system is present. The sexes are united in the same individual. Many forms are parasitic. This is the lowest phylum to assume a pronounced bilateral symmetry. The Nemertinea differ from the other orders of this phylum as described above in the possession of an anus, a blood vascular system and a protrusible oesophagus. The nemer tines are covered by a very slimy secretion. Fossil flat- worms are extremely rare ; they are known from the Pennsylvanian to the present day. Derivation of name. — Greek platys, flat, -f helmins, worm, referring to the flattened appearance of the body. Living examples are the Planaria (fresh water flat- worm), Distomum hepaticiim (liver-fluke, parasitic in sheep), and Tcenia solium (common tape-worm, parasitic in man and the pig)- PHYLUM V, NEMATHELMINTHES (THREAD-WORMS) Body unsegmented, long and cylindrical, with mouth and anus at opposite ends. Sexes usually separate. Mostly para- sitic. Fossils extremely rare. A few examples of this and the preceding phylum have been found fossil as parasites upon insects from the upper Paleozoic coal measures and the Tertiary amber. 140 ANNULATA (RING-WORMS) 141 A fossil looking much like the living round-worm Sagitta has been found in the Middle Cambrian shales of British Columbia. Derivation of name. — Greek nema, thread, + helmins, a worm, referring to the round thread-like body. Living examples are A scar is lumbricoides (the round-worm from the small intestine of man), Oxyuris vermicularis (the pin-worm infesting the rectum of man), Trichina spiralis (para- sitic in man and the pig) and Gordius (the hair-worm ; parasitic in asexual generation, free in sexual ; in the latter it is often 15 cm. long by 5 mm. in diameter and popularly is supposed to be derived from horsehairs which have fallen into the water). PHYLUM VI, TROCHELMINTHES (WHEEL-WORMS) All Trochelminthes, except the few belonging to the slightly related orders Gastrotricha and Dinophilea, belong to the wheel- worms (order Rotifera). These are microscopic in size, being the smallest of all animals except the Protozoa. The anterior end is surrounded by many variously arranged cilia, often in a circle, by means of which the animal moves. Body unsegmented. The oesophagus has a chitinous masticating apparatus. Anus present. Sexes separate. Few species are parasitic. Unknown in the fossil state. Derivation of name. — Greek trochos, wheel, + helmins, worm, referring to the successive movement of the cilia at the anterior end of the body which gives an appearance of rotation. Living examples are Branchionus (abundant in ponds and ditches) and Rotifer. PHYLUM Vn, ANNULATA (RING-WORMS) All, except the class Gephyrea, have a ciliate, elongate body, with mouth at one end and anus at the opposite ; the bilaterally symmetrical body is divided by ring-like constrictions into a series of segments representing a like segmentation within, where each segment contains a portion of the digestive canal, a pair of 142 AN INTRODUCTION TO THE STUDY OF FOSSILS nephridia, a pair of nerve ganglia from the ventral chain and blood vessels. The nervous system consists of a dorsal brain connected around the mouth with the anterior end of the double ventral nerve cord. Paired excretory organs (nephridia) conduct the nitrogenous waste matter from the general body cavity (coelome) to the exterior. Derivation of name. — Latin anmilus, a ring, referring to the ring-like constrictions of the body. The annulata are divided into the four following classes : A. Archi-annelida Living. A primitive class of annulata. Unknown in the fossil state. B. Hirudines Living. Including the genus Hirudo, the leech. Unknown fossil. C. Gephyrea Living. With larva similar to that of the Chaetopoda. Unknown fossil. D. Chaetopoda Cambrian to present. CLASS D, CH^TOPODA Type of the class, Nereis virens (Fig. 55). This form lives in sandy or muddy beaches, usually between tide levels, under rocks or among seaweeds ; at times it reaches a length of over eighteen inches. It inhabits a- burrow which it makes firm by cementing the sand particles of the wall to- gether with a mucilaginous secretion. This common form ranges from Long Island to Labrador, to Great Britain and Norway. Its body, rounded above and flattened below, is divided by ring-like constrictions into a series of segments. Each segment, except the most anterior (head segment) and most posterior (tail segment), bears externally at the sides of the body, a pair of outgrowths, — the fiapper-like gill-feet or parapodia, which aid in creeping or act as oars in swimming. The parapodia are strengthened by chitinous rods extending outwards from the body and are bordered by several bundles of chitinous bristles. ANNULATA (rING-WORMS) 143 The head segment consists of two distinct portions, — the anterior of which bears dorsally four simple eyes and anteriorly a pair of slender tentacles or feelers and a pair of thick palps ; Fig. 55. — The common carnivorous worm, Nereis virens from Massachusetts Bay. A, entire worm. B, a paddle (or parapodium, — much enlarged) from the fifty- fifth segment. C, the head of another specimen, showing the toothed jaws ex- tended, an., anus; e., eyes; j., jaws; p., palp; par., parapodium; seg., seg- ments or divisions of body ; L, tentacles ; /./., terminal feelers. (A and C X 5.) the posterior portion bears antero-laterally four pairs of tenta- cles. The tail segment bears merely a pair of long terminal feelers. The body is inclosed in a very thin layer of chitin secreted by the epidermis beneath it. Beneath the epidermis are circular muscles by which the worm can diminish its diameter, while beneath these are four longitudinal muscles which can diminish its length ; the latter are arranged in two pairs, a dorso-lateral and a ventro-lateral pair. Besides these there are muscles to move the parapodia. Its food consists of both plants and animals, but especially the latter. It is active and voracious, eating especially crus- taceans and other worms. At night it leaves its burrow, swim- ming actively about in search of food, at which time many of these worms are eaten by fishes. The mouth is situated at the end of the head upon the under side ; through this Nereis can thrust out the anterior portion of its oesophagus, by a process of rolling inside out as with the finger of a glove. This thrust- out portion, the proboscis, is provided with two laterally placed, 144 ^N INTRODUCTION TO THE STUDY OF FOSSILS strong, notched, black chitinous jaws. After seizing its prey with these jaws, the proboscis is rolled in again and the jaws then tear the food into pieces. The food next passes through the narrow oesophagus, into the long, straight intestine ; the anus is at the posterior end of the tail segment. The intestine is regularly narrowed, corresponding to the surface constrictions. Into the oesophagus, from the glands at its sides, is poured a fluid, prob- ably digestive in function. From within outward the walls of the intestine consist of (i) a layer of epithelial cells, (2) a layer of circular muscles, (3) a layer of longitudinal muscles and (4) a surface membrane. The muscles aid the forward movement of the food, while the innermost layer probably aids in absorbing the digested portions of the food. Since both the anterior portion of the digestive canal to the beginning of the oesophagus, and the posterior portion within the tail segment are developmentally invaginations of the external surface they are similarly lined with chitin. The blood, of a bright red color, is carried in two main blood vessels, a dorsal tube carrying it forward and a ventral tube moving it backward ; connecting these two are loops in each segment and from these loops branches are given off to the diges- tive canal and to the parapodia. There is no distinct heart, but in the walls of most of the blood vessels are rings of muscles which, contracting in succession, move the blood forward; the walls themselves are likewise contractile. These wave-like contractions move the blood from behind forwards in the dorsal vessel and from before backwards in the ventral vessel. Respiration takes place through the entire body surface but especially through the leaf-shaped gill-lobe attached to the upper side of each parapodium ; these lobes are green at the head end of the body but bright red at the middle and posterior parts. While the excretion of CO2, etc., takes place largely through the gill-lobes of the parapodia, the nitrogenous waste (uric acid, etc.) is carried off by a pair of curved tubes {nephridia) in each segment. ANNULATA (rING-WORMS) 145 The nervous system consists of a bilobed dorsal ganglion, or brain, situated in the anterior part of the head, connected around the mouth with the anterior end of the ventral nerve cord which extends to the posterior end of the body. This cord is in reality double, each part with a separate sweUing or ganglion in each segment, but both united into one by a common covering. The sense organs include the tentacles and cirri as probable organs of touch, the palps used in testing food, and the four simple eyes. Each eye consists of (i) the outer cuticle, the continuation of the body chitin, (2) the cornea, the flattened cells of the epidermis, (3) the large gelatinous lens, (4) the retina, composed of many radially arranged cells, one end of each of which is continuous with the optic nerve and the other projects towards the lens as a clear, glass-like rod. The body of each retinal cell is densely pigmented for the absorption of excess light rays. The sexes are separate. At certain times during the summer they swim near the surface and cast the ova and spermatozoa into the water, where union between them later occurs. The fertilized egg develops into the adult through a series of radically different forms, one of which, the trochosphere stage, it possesses in common with mollusks as well as with other worms. Preservable as fossils are the chitinous jaws, trails, excrement and burrows. 1. Examine Nereis, noting the black jaws at the end of the protrusible pharynx, the eyes, body segments, parapodia, bristles. 2. What is the habitat of the animal ? 3. Its food and how procured ? 4. How is the food digested and the waste moved through the digestive canal ? 5. How is the digested food absorbed and carried throughout the body ? 6. Describe briefly (a) respiration; (b) excretion; (c) the nervous system ; (d) sense organs. 7. What are the principal muscles and their uses? 8. What fossil record can Nereis leave of itself ? 146 AN INTRODUCTION TO THE STUDY OF FOSSILS Summary of CHiExopoDA Annulata with few or many bristles attached to the sides of the body (whence the name from Greek chaite, bristle, + pous {pod), foot). This class includes (a) the earthworms and their allies, unknown as fossils, {b) Nereis, Prioniodus, and other car- nivorous allies and (c) the vegetable-feeding tube builders. The tube-building worms inhabit a tube of their own manu- facture ; these tubes may be formed of lime carbonate, of agglu- tinated particles of sand, etc., or they may be membranous or leathery. These animals have short parapodia which are never used for swimming, and they are devoid of jaws. They include Serpula and Spirorbis. The Chaetopoda are known from the Cambrian to the present. Piioniodus (Fig. 56). Ordovician-Devonian. A jaw of this form, the only portion found fossil, consists of a narrow basal part which supports many, usually five to twenty, small teeth, besides a long tooth situated anywhere from the middle to the end of the basal portion. This long tooth is always continued below the basal part. These jaws prob- ably corresponded in position and function to the jaws of Nereis. The name, from Greek prion, a saw, + odous, a tooth, refers to the saw-like arrange- ment of the teeth. Very many such cone-shaped teeth, found in the Paleozoic from the Cambrian to the Pennsylvanian inclusive, have received the general name of conodonts. Some of them may be fish teeth. Fig. 56. — A conodont, an imperfect jaw probably of an annelid worm, Prioniodus, from the Genesee (De- vonian) of New York. The projec- tions were pointed ; three of these have been restored. Enlarged; true size indicated by line below. ANNULATA (RING-WORMS) 147 I.' Sketch specimen, enlarging it three times. 2. What is the significance of the name ? 3. What general name is applied to all such teeth ? 4. In what part of the living animal were these ? their function ? Fig. 57. — A tube-building worm, Spirorbis borealis Daudin, belonging to the class Chaetopoda, abundant upon seaweed, etc., off the New England coast. The small one to the right is natural size. The middle of the enlarged three is a section of the shell. Spirorbis (Fig. 57). Ordovician to present. Minute, calcareous, spiral tubes (whence the name from Latin spira, spire, + orbis, circle). These tubes are cemented by their fiat underside to some foreign object. 1. Sketch a tube. 2. How could the body of the animal within cement this to some foreign object ? 3. Could the animal leave its tube and later return to it? PHYLUM VIII, ECHINODERMATA Typically radially symmetrical marine animals with a skele- ton of calcareous plates or spicules embedded in the skin. The arrangement of the skeletal plates and of the internal organs is usually pentamerous, the numeral five being thus the governing number of the echinoderms. They are likewise characterized by the presence of a water vascular system which functions in respiration and movement. They represent an advance upon the Coelenterata in the pres- ence of a digestive tube distinct from the body cavity (coelome) , in their more highly developed nervous system, in the possession of a blood vascular system and in an almost exclusively sexual mode of reproduction. The seven classes of the Echinodermata form a more or less closely related group. If the comparison is made with consid- erable latitude, the arms of the starfish and crinoid are homolo- gous to the ambulacra of the cystoid, blastoid and echinoid ; moreover, if the starfish be placed with mouth uppermost, the lower side of the central disk corresponds to the base of the cys- toid, blastoid, and crinoid, while the upper side with its central mouth and radiating ambulacra is similar to the upper side of these classes, and internally the position of the ambulacral, blood vascular, and nervous systems is then similar ; in echi- noids, a like orientation with the starfish may be made by bend- ing the arms of the latter until they almost meet dorsally. The three classes, — cystoids, blastoids, and crinoids, — the individuals of which are usually fixed to some foreign object, are of all the Echinodermata the most intimately related. The blastoids are nearest to the cystoids, the hydrospire prob- ably corresponding to the pore-rhombs, while the position of 148 ECHINODERMATA 149 mouth and anus is approximately the same in both. The hydro- spires of blastoids are likewise correlated with the pores beneath the arm bases of certain crinoids, such as Batocrinus, The Blastoidea and Crinoidea have probably descended from the Cystoidea, while if a common ancestor for all the Echino- dermata, both fixed and free, be sought, it would possibly be found in the primitive cystoids, the Edrioasteroidea (see p. 157). Derivation of name. — Greek echinos, hedge-hog, + derma, skin, in allusion to the spines possessed by many of the members of this phylum. The Echinodermata are divided into the following seven classes : — Page A. Cystoidea iS4 B. Blastoidea 157 C. Crinoidea 159 D. Asteroidea 163 E. Ophiuroidea 165 F. Echinoidea 165 G. Holothurioidea 171 Type of the phylum Echinodermata, Asterias forbesi, the starfish (Fig. 58). Asterias forbesi ranges from Maine to the Gulf of Mexico, but is very common only south of Cape Cod, living from high tide line to a depth of one hundred feet. In summer and autumn it lives in rocky places in shallow water, but seeks greater depths in winter. The starfish is a free-moving animal, consisting of five rays or arms united broadly to a central portion, the disk. The mouth is situated in the center of the under or ventral side of this disk and from it radiate five grooves, one in the middle of each arm. These grooves are called the ambulacral grooves, or ambulacra. Into each of the ambulacral grooves project four rows of soft tubular bodies with sucker-like extremities. These are the tube- feet, the locomotive organs of the animal, and they form a part ISO AN INTRODUCTION TO THE STUDY OF FOSSILS of the water vascular system which is especially characteristic of the echinoderms. This system consists of a series of tube- like passages filled with sea water. The water is admitted through a finely perforated plate, the madreporite, situated on the dorsal side near the junction of two of the arms. From the Fig. s8. — A four-months-old starfish, Asterias forhesi, from Narragansett Bay, Mass. Natural size, mad., madreporite. (From Mead.) madreporite an S-shaped tube, the madreporic or stone canal, descends to the ventral side of the animal and connects with a five-sided ring-like canal surrounding the mouth. From this ring-vessel radiate the five straight ambulacral vessels to the extremities of the five arms. Along each of these radial tubes are given off the four rows of tube-feet. Each of these tube-feet is a small muscular tube, closed at one end and expanded at the other into a bladder-like amptdla. The ampullae are inside the ECHINODERMATA 15 1 arm, protected by the dermal plates, while the small closed end extends between the plates, protruding out into the arm furrow and ending in a disk-like expansion. The sea water is admitted from the radial ambulacral vessel of the arm into the ampulla ; by the contraction of this it is forced into the corresponding tube-foot, which thus becomes greatly lengthened. When the foot is thus extended and comes into contact with a stone or other solid object the water is withdrawn from it, the middle of its tip is drawn inward, forming under it a vacuum, and thus the disk-like end of the foot is converted into a sucker which clings to the rock. When water is again forced into the foot by the ampulla, the hold of the sucker is relaxed. Thus the many tube-feet acting independently reach forward in the general direction of locomotion, attach themselves to some foreign object, and through contraction pull forward the entire body with a slow gliding motion, while the other feet already contracted loose their hold and then reach forward. A fair speed is six inches a minute. Although a starfish can move in any direction, it usually proceeds with the arm lying immediately to the left of the madreporic plate in advance. The skeleton or test consists of many calcareous plates em- bedded in the sub-epidermis (mesoderm), which, except at the mouth, completely surrounds the body. Since bands of muscular fibers extend between all contiguous plates, the arms and disk are movable. The protective spines are covered only by the epidermis. The chief food of the starfish is moUusks (especially mussels, clams and oysters), barnacles, worms, and small crustaceans. In securing its food, such as a clam, it folds its arms about its prey, attaching its hundreds of tube-feet to the valves of the shell, and through the steady pull thus exerted tires the large adductor muscles of the mollusk. Experiment has shown that a large starfish can exert a steady pull of over two and a half pounds. Between the valves thus opened the starfish rolls its very dis- tensible stomach in the form of a thin sheet spread over the 152 AN INTRODUCTION TO THE STUDY OF FOSSILS soft tissues of its prey. Then the great digestive glands in the upper part of the stomach and in the arms pour out their secre- tion through the tubular passage remaining in the center of the sheet, and the food is rendered fluid and absorbed. The stomach then contracts and is rolled back through the mouth into the body. The starfish may live for months practically without food, but when opportunity offers it will eat many mollusks, one immediately after another. It opens gastropods (periwinkle or conch) in a similar manner by attaching the tube-feet to the operculum and shell. The upper, narrow portion of the stomach has long divisions, one extending to the end of each arm. These divisions secrete a digestive fluid which converts starch into sugar, proteids into peptones, and emulsifies fat ; the resultant, chyle, is taken by osmosis into the veins. A vein runs along the digestive tube from the mouth to the arms and forms a circle around each end of the tube ; branches from these traverse the body and each arm. The rings around the mouth open at one side into the general body cavity, the coelome ; hence the "blood" of the coelome and of the blood vessel is the same, a thin fluid consisting of sea water, chyle, and some amoeboid corpuscles. From the upper portion of the stomach, the waste products are conducted out through the anus, w^hich is situated nearly in the center of the dorsal surface of the disk. Respiration takes place (i) through the short, hollow, thread- like processes (dermal branchiae) which extend out through microscopic pores between the plates over the whole body and open directly into the coelome, and (2) by the ambula- cral system, the oxygen entering through the tube-feet and madreporite. The nervous system has three divisions, (i) the epidermal, — a pentagonal nerve ring around the mouth, from each of the five angles of which one radial nerve fiber extends below the radial ambulacral vessel to each eye-spot ; (2) the deep portion, a double pentagon around the mouth, of which each angle sends ECHINODERMATA 153 a nerve to each arm ; and (3) the coelomic, the nerves extending along the top of each arm. The sense organs include that of smell and the so-called eye. At the tip of each arm is a bright red speck, the eye-spot. This is practically nothing but a collection of pigment granules upon the expansion of nerve cord ; since there is no lens there can be no image, and hence the animal can probably distinguish light and color, but not form. The perception of light is probably merely the sensation of warmth due to the absorption of the light rays by the pigment and their consequent conversion into heat. Over the eve is a tentacle similar to a tube-foot, but smaller and without the sucker. Experiments have determined its function to be that of smell, and that the animal is guided to its food more by this sense than by sight. Reproduction is exclusively sexual. The eggs and spermatozoa are discharged into the water in great abundance during the last three weeks of June, although they are also found during the summer and occasionally even during the winter. The eggs after fertilization develop into little transparent larvae covered with waving cilia. At this time their greatest enemy is the menhaden. They swim about slowly near the surface and feed on minute organisms until they attain a length of an eighth of an inch. Then the star shape begins to develop and in a few hours a very small star lies at the bottom of the ocean. These settle on seaweeds and eel grass and begin at once to devour the young clams which have likewise begun life here. It has been found that one of these little starfishes devoured over fifty young clams somewhat smaller than itself in six days. Their growth depends upon the amount of food eaten, and hence the age at which a female begins to produce eggs is said to vary from one to six years. A starfish can regenerate lost arms. I. Sketch (a) ventral view, (b) dorsal view. Label disk, arms, ambulacra, tube-feet openings, mouth, eye spots, mad- reporite, anal plate, spines. 154 AN INTRODUCTION TO THE STUDY OF FOSSILS 2. Give the habitat of Asterias. 3 . How does it move ? 4. What is its food ? Describe how it eats. 5. How is the food digested ? assimilated? waste expelled ? 6. What protection against enemies has Asterias ? 7. Is the skeleton (test) external or internal? Explain. 8. How does the animal respire ? 9. Of what does the nervous system consist ? Its use ? 10. Describe the sense organs. 11. Give very briefly its development from the egg to the adult. 12. How long does it take to mature ? 13. What makes the starfish such an enemy to oyster and clam culture ? 14. In what respects are the echinoderms more highly evolved than the coelenterates ? CLASS A, CYSTOIDEA (CYSTOIDS) Calyx usually stemmed. Mouth nearly or quite central upon the upper (ventral) surface. From the mouth radiate two to five or more simple or branching ambulacra, along which passed food particles to the mouth, probably driven by numerous cilia. These food grooves may be upon the outer surface of the calyx plates, between them, or upon their inner surface, and are rarely extended into free branches, the arms. Anal opening excentric, often closed by a valvular pyramid. Calyx plates usually irregularly arranged, varying in number from thirteen to several hundred ; as a rule a few, or all of the plates, are pierced by pores which are either irregular or arranged in rhombic figures, with half of the rhomb on one plate and half on an adjoining one ; the pores from opposite plates are united by closed straight ducts which may have functioned in respira- tion. Cystoids are the oldest and least specialized group of the Pelmatozoa (which include cystoids, blastoids, and crinoids), and probably represent most nearly the ancestral t3^pe of the three classes. ECHINODERMATA — CYSTOIDS 155 They are extinct, being confined entirely to the Paleozoic. They extend from the Cambrian to the Permian, inclusive, with maximum development in the Ordovician and Silurian. Derivation of name. — Greek, cystis, bladder, + eidos (aid), form, in allusion to the globular shape of most of the species. Fig. 59. — Caryocriniis ornatus Say, from the Niagara shales (^Middle Silurian) of western New York. A, calyx of a large specimen (natural size) with stem and arms missing. B, inside of one of the plates (slightly enlarged), showing the water tubes, with an opening at their inner ends, an., anus, protected by a valvular pyramid; 5/., position of stem; /w., tubes. (After Hall.) Caryocrinus (Fig. 59). Ordovician to Silurian. The principal portion of the body, a sub-globular hollow ball, called the calyx, contained the digestive and blood vascular systems. This calyx was anchored to the ground by a long, jointed stem. The food grooves (ambulacra) radiating from the mouth terminate in six to thirteen feeble arms. Both mouth and food grooves are within the upper part of the calyx. Upon the outer surface of each calyx plate, except the summit one, are five or six single or double rows of pores radiating from its center. Each of these pores is prolonged upon the inner sur- face of the plate into a straight calcareous tube (Fig. 59, tu) which in turn opens by a pore upon a bordering plate. All the tubes 156 AN INTRODUCTION TO THE STUDY OF FOSSILS thus uniting across the straight suture of two contiguous plates form in outline a rhomb, from which these have received 'the name of pore-rhombs. The function of the pore-rhombs is supposed to have been respiratory. Caryocrinus is thus somewhat similar to a starfish turned mouth side uppermost, with an anchoring stalk attached to the dorsal side, the mouth and much of the ambulacra concealed by calcareous plates, and with the ends of the ambulacra branching into free arms. With the mouth concealed, food was of neces- sity urged into it through the ambulacral grooves by the cilia lining them. Since the ambulacra were often concealed by calcareous plates, tube-feet were in all probability absent. 1. Sketch (a) side view, (b) enlarge a plate twice. Label calyx, place for attachment of stem and of arms, plates forming the ventral surface of calyx, pores. 2. What was probably the function of the pores ? 3. Of w^hat did the animal's food probably consist ? How did it procure it ? 4. Compare Caryocrinus to a starfish. 5. What was its habitat? Reasons. 6. What part of the living animal does the fossil represent ? 7. What animals living off our coast are likewise fastened to the ground ? 8. What characters show the aTnO. cystoids to be primitive un- specialized types ? 9. Give the geologic range of the cystoids. an. Fig. 60. — A cystoid, Agelacrinus cin- cinnatiensis Roemer, from the Ordo vician of Cincinnati, Ohio. Top view . , . /^. ^ \ (X 2) showing the curved ambulacra AgClacrmuS {i^\g. OO) (amb.) within which are the covered food grooves. Anus (an.) nearly mar- ginal. (Redrawn from Meek.) Ordovician to Mis sis sip plan. The animal is circular, flat, stemless, cemented by the entire lower (dorsal) surface to a foreign object, usually a brachiopod ECHINODERM ATA — BLASTOIDS 1 5 7 shell. The hard protecting calyx is composed of many thin, flexible and more or less overlapping plates ; these are perforated by pores, which probably had a respiratory function. From the centrally placed mouth, which is covered by four plates, radiate five curved, unbranched, covered food grooves. The anus occurs between two of the food grooves roofed over by a low pyramid of plates. This genus and the many other forms similar to it are often placed together in a distinct class, the Edrioasteroidea, extend- ing from the Cambrian to the Mississippian. 1. Sketch surface view, noting calyx, mouth, anus, am- bulacra. 2. How, probably, did the animal procure its food ? CLASS B, BLASTOIDEA (SEA-BUDS) Calyx ovate, short-stemmed or stemless ; distinct arms ab- sent ; these exist only as pinnules. Around the central mouth are five or ten spiracles which are connected internally with the hydrospires, — canals probably respiratory in function. Some forms have a distinct anal opening ; in others this opening is fused with one of the spiracles. From the mouth radiate five ambulacral areas. The class is entirely extinct and confined to the Paleozoic, ranging from the Ordovician to the Permian. Derivation of name. — Greek blastos, bud, + eidos (oid), form, in allusion to the bud-shaped calyx of most species. Pentremites (Fig. 6i). Mississippian. This differs in general from the starfish in its bud-shaped body (calyx), which was anchored to the ground by a short, jointed stem attached to its dorsal surface ; the mouth, or ven- tral side, was thus uppermost. The calyx inclosed the digestive and blood vascular systems. In the center of the upper surface is a five-angled opening, the mouth, surrounded by five round openings, the spiracles. From each angle of the mouth radiates 158 AN INTRODUCTION TO THE STUDY OF FOSSILS a food, or ambulacral groove, and from this groove branch off smaller side grooves almost at right angles, the whole forming a V-shaped ambulacral area. At the upper end of each side groove is a small pore {marginal pore) ; these pores open upon the inside of the calyx into a cal- FiG. 61. — This blastoid, Pentremites pyriformis Say, was very prolific in the clearer portions of the sea {i.e. Kentucky, Alabama, and Mississippi), which covered much of North America during Kaskaskia (Upper Mississippian) time. A, side view (natural size) with stem missing, as is nearly always the case. B, top view. C, cross section ( X 2) at a-b in Fig. A. amb., ambulacrum ; an., anal opening fused with a spiracle; ba., basal plate; f.gr., food groove; hy., hydrospires (to conduct water from the marginal pores out through the spiracles) ; i.r., interradial plates; m.po., marginal pores; mo., mouth; 5/)., spiracles ; r., radial plates ; st., place of attachment of stem. careous canal looking like a much-folded bag, — the hydrospire, probably respiratory in function. Each of the five pairs of hydrospires from adjoining ambulacra end in one of the spiracles. During life, it is probable that a current of water passed in at the marginal pores, through the hydrospires, and out at the spiracles. Around the marginal pores were long, jointed pin- nules which functioned in straining out the food particles ; this food, probably similar to that of crinoids, was urged down the side grooves by the cilia lining them, and thus down the central groove to the mouth. In exceptionally well-preserved speci- mens the central and side food grooves to the base of the pinnules are roofed over by very minute plates. The position of the pinnules is indicated by minute pits and knobs. Little is known concerning the digestive, blood vascular, and nervous systems ; there is some evidence of radial nerve cords connected with an oral ring, ard of radial blood vessels likewise ECHINODERMATA — CRINOIDS 1 59 connected with an oral ring. The anal opening is fused with the largest spiracle. The calyx has thirteen definitely arranged calcareous plates, — three basals, five large incised radials, and five interradials or deltoids. The plates are firmly united. The structure of the stem is similar to that of the crinoids. Pentremites was exceedingly abundant in the sea which covered most of North America during Mississippian time. 1. Sketch (a) side view, (b) ventral view. Label calyx, mouth, spiracles, ambulacra, marginal pores, anal opening, place for attachment of stalk. 2. Explain the process by which the animal ate. 3. How did it probably respire ? 4. Compare it to a starfish. 5. Give the geologic range of Pentremites. 6. What was its habitat ? 7. What part of the living animal does the fossil represent? 8. Could the animal move ? Reasons. CLASS C, CRINOIDEA (SEA-LILIES) Body, the calyx, more or less globidar, fastened, tem- porarily or permanently, to some foreign object by means of a stalk arising from its dorsal (lower) surface. The ventral (upper) surface bears the mouth, which is usually central, the anus, which is excentric, and the ambulacral grooves. These grooves extend into the more or less complexly branched arms, which are usually bordered with pinnules. Some forms, as Eucalyptocrinus, were attached by roots, some, as Pentacrinus and Ancyrocrinus, anchored themselves to seaweeds and other objects by processes from the lower end of the stalk, and some probably used their stems for coiling around a support. Crinoids range from the Ordovician to the present time, though they were most abundant in the upper Paleozoic. Owing to their gregarious habits, their skeletons form the chief part of great masses of limestone (hence called crinoidal limestone), especially in the Devonian and Mississippian periods. l6o AN INTRODUCTION TO THE STUDY OF FOSSILS Fossil remains of these animals consist mainly of detached portions of stems or scattered calyx plates. Complete forms, preserving calyx, stem, and root, are rare. Derivation of name. — Greek crinon, \\\y,+eidos (oid), form. The stalked forms resemble lilies, as is noted also in the common name of the class, " sea- lilies." Pentacrinus (Fig. 62). Trias sic to present. This form, unlike the starfish, has the mouth, or ventral side, uppermost, while the opposite, or dorsal, side is fixed to the ground by a long flexible stalk. The animal is composed of a globular body (calyx), from the upper surface of which branched arms, and from the Fig 62.-Above stem joints j^^.^^ ^^^^^^^ -^ ^^^^ ^^ ^^^ ^^^^^^ of the cnnoid, Pentacrtnus _ '^ asteriscus M. & H., from Embedded witliin the skin of all parts the Jurassic of Montana. ^^^ ^ calcarcous platcs forming a To the left the surface •' ^ ^ '^ ^ view of a joint (natural Strong protective skeleton. The stalk is size); to the right five ^^^^ ^^ grooved disks, resting one jomts, side view. Below, a r- o jo modern crinoid, Pentacri- upon the Other like a pile of coins, and nus caput-meduscB (much pierced at the center by a canal contain- reduced), from the Gulf ^ ^ -^ of Mexico. This shows ing a prolongation of the nervous and the arms (concealing the blood vascular svstcms. Small branches, calyx) and the upper por- _ _ •' ^ ^ ' tion of the stem. The the cirri, whose function is doubtful, are last is reproduced from j^.^^^ ^^ f^.^^^ ^^^ ^^^^ ^^^ ^^^^ ^^ '^^_ Lucas Animals before ^ man in North America." ternal and external structure similar to Copyright, 1902, by D. ^j^^^ ^f ^j^^ ^^^^^ ^^ ^^^^ ^ ^^^_ Appleton and Co. ' ^ ably, the stalk was attached to the ground by a branching root; more generally it was free, being merely anchored to seaweeds, etc., by the entwining of the cirri ECHINODERM ATA — CRINOIDS 1 6 1 at its lower end. The stalks are very long, attaining at times a length of at least twenty feet. The calyx is made up dorsally of calcareous plates definitely arranged ; the plates upon the ventral surface are without definite order. All the plates are firmly united, forming a rigid skeleton. The mouth occupies the center of the upper surface and from it radiate five open amxbulacral or food grooves to the tips of the arms. These arms, unlike the usually simple ones of the starfish, branch repeatedly, each branch in turn giving off many short side branches or pinnules. The ambulacral grooves branch correspondingly. These grooves are lined with cilia by the aid of which the food, chiefly diatoms, pro- tozoons, and microscopic crustaceans, is urged into the mouth. The ambulacral system here, as in the starfish, forms a ring around the mouth and sends a ray to each pinnule ; connected with this ring are several ciliated, branched water-tubes opening into the coelome. Into this coelome, the body cavity, water enters from the exterior by means of minute water-pores through plates on the ventral surface. Small, distensible tube-feet, the tentacles, are present ; they, however, lack suckers, and are not locomotor but merely tactile and respiratory in function. The water-pores and water-tubes represent the madreporite and its canal of the starfish. The mouth opens through an oesophagus into a wide stomach, thence into the intestine, which coils inside the body wall, but does not have extensions into the arms. It opens by the anus through a tube eccentrically placed upon the upper (ventral) surface. The blood vascular system consists of a ring around the oral end of the digestive canal, giving off radial vessels to the arms and the stalk. The nervous system consists of (i) the ambulacral portion, — a ring around the mouth from w^hich pass series of nerves to arms and pinnules through the base of the ambulacral grooves ; and (2) the axial portion, — a five-angled organ beneath the basal plates at the junction of calyx and stalk, from which radiate 1 62 AN INTRODUCTION TO THE STUDY OF FOSSILS nerves through the center of the arm and pinnule plates and to the stalk. A transverse section through an arm would thus show a blood tube, a water tube and a nerve cord directly be- neath the food groove, while deep within the calcareous plate is lodged a second nerve cord. The sexes are separate. The dilated pinnule bases lodge the ovaries and testes. The stalk is five-sided throughout in ancient fossil species (e.g. P. asteriscus) but in living forms only near the calyx. New plates are added directly beneath the calyx ; these are in living Pentacrinus at first five-sided like the entire stalk of lower Meso- zoic species ; but later they become round. These changes, in which the animal recapitulates its ancestry, may be noted in a single individual from the small plates directly beneath the calyx to the large ones at the lower end of the stalk. The young stem joints are more porous than older ones, and therefore not so apt to be preserved fossil. The range of the genus is from the Jurassic to the present. The symmetrically pentagonal stem joints of Pentacrinus as- teriscus are very abundant in the Jurassic of the western part of North America. Living forms occur chiefly in the Caribbean Sea and the Pacific Ocean. 1. Sketch side view, noting calyx, arms, pinnules, stalk. 2. Compare it to the starfish. 3. How and what does Pentacrinus eat ? How breathe ? 4. Of what does the nervous system consist ? 5. Could the animal move ? Reasons. 6. Is the skeleton external or internal ? Illustrate by means of a plate of the stalk. 7. What is the significance of the name crinoid ? 8. What is the evolutionary significance of the fact that the plates of the stalk immediately below the calyx are five-pointed, but later become rounded ? Euc£ilyptocrinus (Fig. 63). Silurian, rarely Devonian. Calyx with a deep concavity at the stem end. Attached to the elongate ventral portion of the calyx and extending its full ECHINODERINIATA — STARFISHES length are ten vertical partition plates ; in each of the ten compart- ments thus formed are lodged two arms, which unlike Pentacrinus never extend upward beyond the calyx. 1. Sketch side view, noting calyx, vertical partitions, arms if preserved. 2. In what conspicuous feature does this genus differ from most other crinoids ? CLASS D, ASTEROIDEA (STARFISHES) Body free, star-shaped, with a cen- tral disk and hollow arms (usually five in number), each containing a prolongation of the organs of the body. Movement is by means of the tube-feet which project between the plates from the five ambulacral grooves radiating from the mouth. Asteroidea range from the Cam- brian to the present. Living ex- amples include Aster ias vulgaris and Asterias forbesi (p. 149), the common starfishes of the Atlantic coast, the former north and the latter south of Cape Cod. There are many tropical species. Derivation of name. — Greek aster, star, -h eidos {old), form, in allusion to the star-shaped body. Paleaster (Fig. 64). Ordovician to Mississippian. Differs from Asterias in having the two rows of ambulacral plates Fig. 63. — Eucaly ptocrinus cras- sus Hall, from the Middle Silurian of Indiana, a., arms ; c, calyx or cup; h. f., hold fasts, the rootlike basal part for attachment to the ground ; St., stalk. Slightly reduced. (From Hall.) 1 64 AN INTRODUCTION TO THE STUDY OF FOSSILS Fig. 64. — Paleastcr eucharis Hall, from the Devonian of New York. A, dorsal side, showing the madreporite {mad.) . B, ventral side, showing the centrally placed mouth and the large marginal plates (mar. p.). (After Hall.) ECHINODERMATA — SEA URCHINS 165 but slightly inclined to each other, the plates from the opposite sides alternating, in the very large marginal plates and in having two, instead of four, rows of tube-feet. 1. Sketch specimen. 2. Is it a dorsal or ventral view ? 3. How does it diilfer from Asterias? ^0m CLASS E, OPHIUROIDEA (BRITTLE STARS) Ambulacral and digestive systems confined to the central disk; otherwise in external appearance much like the Aster- oidea. Movement by means of the slender, rounded arms which are quite sharply marked off from the central disk. No anal opening present. Madreporite ventral. The range of the class is from the Ordovician to the present. Living forms are more com- monly inhabitants of deep than of shallow waters. Ophiopholis aculeata (Fig. 65), the ''brittle starfish," is abundant at a depth of one to one hundred feet in rocky crevices from the coast of New Jersey to the Arctic Ocean and is likewise common on the Pacific coast and in north- ern Europe. CLASS F, ECHINOIDEA (SEA URCHINS) Free-mo\ing animals, usually with a globular, or disk-shaped, body. Skeleton {test) rigid, formed of firmly united calcareous plates, or more or less flexible with imbricating plates, covered with movable spines. Mouth ventral and central, or anteriorly eccentric, with (except in the adult spatangoids) a compHcated Fig. 65. — Ophiopholis aculeata Gray, from the coast of New England. The brittle starfish. Dorsal view (xi). (From Verrill and Smith.) 1 66 AN INTRODUCTION TO THE STUDY OF FOSSILS masticating apparatus, the Aristotle's lantern. Madreporite dorsal, in the right anterior genital plate ; this plate orients the sea urchin, the antero-posterior axis passing through the ambulacrum on its left and through the opposite interambula- crum. The anal opening is dorsal, in the posterior inter- ambulacrum. Straight or variously arranged ambulacral areas run from the dorsal to the ventral surface. Movement is by means of the elongated tube-feet which pass through, not between, the plates. Many forms in addi- tion move by means of their spines, often quite rapidly. Sea urchins are gregarious, frequently occurring in such abun- dance as to pave the surface of the rock and the bottom of tide pools in sheltered places. On exposed coasts, many forms bore cavities by their teeth or by absorption into calcareous and non- calcareous rocks. Common examples are Strongylocentrotus, on the Atlantic coast north of Cape Cod; Arbacia, on the Atlan- tic coast south to Florida; Echinarachnius, the '' sand dollar," on sand beaches from New Jersey northw^ard and on the Pacific coast. Echinoids are known from the Ordovician to the present. Derivation of name. — Greek echinos, a hedge-hog, + eidos (oid), form, referring to the spines so characteristic of all members of this class. Strongylocentrotus (Figs. 66, 67). Upper Tertiary to present. This differs from the starfish in its globular form, which is slightly compressed dorso-ventrally. The calcareous plates are firmly fitted together like a mosaic, forming a rigid shell. The entire surface, except the region around the mouth, is thickly studded with many rounded tubercles, to which are attached solid spines which are movable by muscles on ball and socket joints (Fig. 67, 5). Corresponding to the five ambulacral grooves of the starfish are five slightly expanding amhulacral areas (am- bulacra) extending radially from near the center of the dorsal to the ventral side. Each ambulacrum consists of two narrow ECHINODERMATA — SEA URCHINS 167 j^^t^^:^ amb.. Fig. 66. — The common sea urchin, Slrongylocentrotus drobachiensis Say, from the coast of Maine. Entire individual, dorsal view (with spines, etc., removed from half of the shell (test)). Below is the central dorsal area with ornamentation omitted, a., anus, the large black spot within the periproct (the area within the circle of genital plates and protected by many small plates) ; amb., ambulacrum ; g., genital plate at tip of each interambulacrum, perforated by the genital opening, — the large black spot; int. amb., interambulacrum; mad., madreporite; oc, ocular plate at tip of each ambulacrum. 1 68 AN INTRODUCTION TO THE STUDY OP FOSSILS columns of plates through which the long, sucker-bearing tube- feet protrude (Fig. 67, A t.f.) ; the middle of the area is without pores for tube-feet and bears numerous spines. The tube-feet number about 1800, and can be protruded beyond the longest Fig. 67. — An enlargement of a small portion from Fig. 66. A, an enlargement of the seventh and eighth interambulacral plates, and the adjoining ambulacral ones, counting from the first ocular to the right of the madrepore. B, a single spine ( X 5), showing its ball-and-socket joint and the attachment of the muscles to move it. b., base of spine ; m., muscles to move the spine ; ped., the small grasping pedi- cellariae with the minute pincer-like heads; sp., large and small spines; /./., tube- feet ending in suckers and capable of expansion to double the length shown here, or of contraction to far within the spines ; tu., tubercle. spines. Between each set of two ambulacra are the inter- ambulacra, — broad, spine-bearing areas composed of two col- umns of plates. The water-vascular system is similar to that of the starfish, except that the radial canals giving off the tube-feet lie within, not without, the test. Growth takes place by the increase in size of the plates and by the addition of new plates dorsally at the ends of the ambu- lacra and the interambulacra. A complicated apparatus, called Aristotle's lantern, is connected ECHINODERMATA — SEA URCHINS 169 with the digestive system. It consists principally of five enameled teeth meeting in a point ; they project slightly out of the mouth, and are moved by a complicated set of muscles. The teeth and muscles are supported by five pyramidal plates which with their connections (epiphyses, bases and compasses) form the skeletal part of Aristotle's lantern. These teeth are used to grind the food into bits. A wide digestive tube extends from the mouth in the center of the ventral (lower) surface to the anus in the center of the dorsal (upper) surface, winding around the inside of the test. There is no such differentiated stomach, nor radial divisions of the digestive system, as occur in the starfish. The five double rows of long, slender tube-feet enable the animal to cling to the rocks over which it slowly glides in search of the algae and small organisms on which it lives. Sea urchins are usually vegetable feeders. The hlood vascular circulation is very similar to that of the starfish, having in addition two large intestinal veins parallel to the intestine. The blood has about the same composition as that of the starfish. Respiration is effected mainly by the upper end of the digestive canal and by the shrub-like gills at the ventral margin of the test. The nervous system is similar to that of the starfish, and there are present, likewise, five eye spots at the tips of the ambulacra in the ocular plates. At the tip of each interambulacrum is a genital or basal plate in which are openings for the extrusion of the repro- ductive elements. Through these pores the eggs and sper- matozoa are cast out into the water during summer, where after union they rapidly develop into tiny translucent bi- lateral larvae. These larvae swim about and feed on smaller creatures for several weeks, finally developing a minute, globu- lar, radial sea urchin at the posterior end. In a few hours the larval portion becomes absorbed and leaves the minute sea urchin to drop to the sea bottom. lyo AN INTRODUCTION TO THE STUDY OF FOSSILS Strongylocentrotus drobachiensis is found in the deep waters of Long Island Sound, in shallow tide pools north of Cape Cod, and covering the rocks upon the Maine coast. It extends into the Arctic Ocean and occurs also on the north Pacific coast. B Fig. 68. — The Paleozoic sea urchin, Melonechinus muUiporus (Norwood and Owen) which was very abundant in the shallow seas covering much of Missouri during the St. Louis (Upper Mississippian) time. Dorsal view ; slightly reduced in size. A, C, E, G, and / are the interambulacra ; B, D, F, H, and / the ambulacra. At the tips of the interambulacra are the genital plates, each with three pores ; the ocular plates at the tips of the ambulacra are much smaller than the genitals. (From Jackson.) ECHINODERMATA — SEA CUCUMBERS 171 1. Sketch (a) side view, (b) ventral view, (<:) dorsal view. Label ambulacra, interambulacra, mouth, anus, teeth if present, openings for tube-feet, madreporite, ocular and genital plates. 2. Compare it with a starfish. 3. How and what does Strongylocentrotus eat ? 4. Describe its respiration. 5. How does the animal move? 6. How does it increase in size ? 7. Of what use are the spines? Make a sketch illustrating how they are moved. 8. In what directions may a spine be moved? 9. Can Strongylocentrotus chmb ? 10. Give the geologic range of Echinoidea. Melonechinus multiporus (Fig, 68). Mississippian. Test very large, spheroidal, marked vertically by elevated, melon-like ribs, which are due to the thickening of the plates and are hence hardly recognizable in internal molds. Ambu- lacra broad with ten columns of plates at widest part ; inter- ambulacral areas with eight or nine columns of plates. Tubercles small, numerous ; spines minute, needle-like. This species was very abundant in the St. Louis (Mississippian) seas of Mis- souri. The earliest species of Melonechinus had fewer columns of plates than the later ones. (This genus was formerly called Melonites.) 1. Sketch side view, noting ambulacra, interambulacra. 2. Was the living animal attached or free ? CLASS G, HOLOTHURIOIDEA (SEA CUCUMBERS) Free, with elongated, more or less cylindrical body. Mouth and anal opening at opposite ends. The body differs from that of the starfish in being greatly drawn out in the direction of the line joining mouth and anus ; this line is likewise the direc- tion of movement. The ventral surface is parallel with the axis joining mouth and anus, not at right angles to it as in the 172 AN INTRODUCTION TO THE STUDY OF FOSSILS starfish, and is furnished with rows of well-developed, functional tube-feet. The place of tube-feet on the dorsal side is taken by papillae lacking suckers. Ten large, branched, contractile tentacles, w^hich are probably enlarged tube-feet, surround the mouth. After the manner of some worms, holothurians devour sand and mud, deriving their nourishment from the organic particles contained in them. The leathery body is usually supported only by scattered calcareous spicules of various shapes, and possesses no true skeleton. Usually the spicules alone are capable of preserva- tion as fossils ; these are known from the upper Paleozoic to the present, but representatives showing the impression of the entire body have been described likewise from the Middle Cambrian of British Columbia. Holothurians are widely distributed at present through all seas, with a habitat extending from shallow to deep water, in tide pools, on rocks, or in the sand or mud. Derivation of name. — Greek holothourion, a water-polyp, -f eidos (oid), form. 1. Name the seven classes of Echinodermata, giving very briefly the distinguishing characteristics of each ; likewise a living and fossil example of each when possible. 2. What do these classes possess in common that they should be placed in the same phylum ? 3. How do the Echinodermata differ from the Coelenterata in the following characters : (a) habitat, (b) protecting and supporting skeleton, (c) locomotion, (d) food, (e) its capture, (/) its intake, (g) digestion, (h) blood circulation, (i) excretion of waste, (j) respiration, (k) nervous system, (/) sense-organs, (m) reproduction, (n) geologic range? 4. Compare the arms of a starfish to corresponding structures in the other classes. 5. In what class would you look for the ancestor of the stalked forms ? For the ancestor of all Echinodermata ? 6. In what respects do the Echinodermata show advance over the Coelenterata ? PHYLUM IX, MOLLUSCOIDEA The MoUuscoidea are aquatic, usually marine animals with a well-developed digestive canal. There is a tentacle-bearing ridge (lophophore) surrounding the mouth. This ridge is partly respiratory in function. A nerve ganglion is present dorsal to the oesophagus. The soft parts of the body are sup- ported and protected by a calcareous, corneous or membra- nous covering. Derivation of name. — MoUuscoidea > English Mollusca -h Greek eidos (old), form. The external, bivalve shell of the class Brachiopoda bears some resemblance to the molluscan shell of the class Pelecypoda. The MoUuscoidea are divided into the following classes : Page A. Bryozoa " 173 B. Phoronida 181 C. Brachiopoda 181 CLASS A, BRYOZOA Type of class, — Bugula avicularia (Kving) (Fig. 69). The most common species on the Atlantic coast, from North Carolina to Maine is Bugula turrita. This may be used in the laboratory in place of B. avicularia. This is a colonial form, growing in tufts two or three inches long on piles or rocks on the seashore in all parts of the world. The colony {zoarium) is made up of erect stems, attached by root-like fibers to the rock or other support. Each stem con- sists of four parallel rows of closely arranged zooscia, — the individual cups. On nearly all zooecia is an appendage, the avicularium, with very much the appearance of a bird's head, 173 174 AN INTRODUCTION TO THE STUDY OF FOSSILS .-ten. which is in almost constant move- ment and whose function is rather problematical, though it is doubtless somewhat protective. Protection. — Each individual con- sists externally of a chitinous cup, with the broad opening extending outward from the colonial stem. (The material is closely akin to the true chitin of the Arthropoda.) This cup of chitin is the hardened and thickened cuticle of the entire animal except the anterior portion, or introvert (Fig. 69). Into this hard-walled cup muscles can with- draw the soft-walled anterior body portion, while the contraction of the sphincter muscle at the orifice com- pletely closes the cup and protects the inclosed soft parts. By these muscles likewise the tentacles can be swayed in any direction. The digestive system is U-shaped with mouth and anus both anterior, and is suspended within the pouch- like coelome or body cavity of the animal. The whole anterior por- tion of the body, the introvert, has walls of thin cuticle continuous with the walls of the chitinous cup and in the contracted state of the ani- mal it is folded back within the cup Hke the turned-in finger of a glove. When, however, the animal expands, the introvert is pushed out through Fig. 69. — Bugula avicidaria. Diagrammatic longitudinal sec- tion through a single individ- ual, expanded from its pro- tective cup of chitin, in the position of feeding, an., anus; avic, avicularium; funic, fu- niculus ; g. mus., one of the mus- cles attaching the stomach to the walls of the cup; int., in- testine ; intr., introvert ; loph., lophophore ; mo., mouth ; oe., oesophagus ; ov., ovary ; ph., pharynx; ret., one oi the mus- cles to retract the introvert within the cup ; st., stomach ; ten., tentacles; tes., testis. Much enlarged. MOLLUSCOIDEA — BRYOZOA 175 the opening of the chitinous cup. In this expanded condition, the position of feeding, the mouth is seen to occupy the ante- rior end of the introvert ; it is surrounded by a circular ridge, the lophophore, bearing about 14 tentacles. The tentacles sur- rounding the mouth are densely covered with cilia on their inner surfaces and the vibration of these cilia drive currents of water towards the mouth. The particles of food in these water-currents, as well as those caught by the prehensile tenta- cles, pass through the mouth into a wide pharynx, thence through a short oesophagus into the stomach. It is here that the digestive canal makes its U-shaped bend, for the intestine rises from the forward end of the stomach and extends in an anterior direction, near and parallel to the oesophagus, to its termination in the anus, which is near the mouth, but outside the circle of tentacles. There are no blood vessels and no excretory organs. The digested food passes through the digestive canal into the pouch- like body cavity (coelome), which contains a fluid in w^hich are colorless corpuscles, the leucocytes. The movement of this fluid is effected largely by the movements of the animal. The collection of the nitrogenous waste matter is probably carried on largely by these leucocytes. The tentacles are the chief organs of respiration; they are hollow, forming narrow prolongations of the coelome and prob- ably effect a transfer of the fresh oxygen of the sea water for the effete gases of the body cavity. No nervous system has been traced in Bugula. In some other genera it takes the form of a small, rounded ganglion be- tween the mouth and the anus which gives off nerves to various parts of the body. Aside from the tentacles, which may be organs of touch, there are no organs of special sense in any of the Bryozoa, except possibly the epistome of the Phylactolae- mata ; this is a fold of the lophophore which closes the mouth and may in a manner taste what passes into the mouth. Each zooecium is lined internally by a cellular substance, 176 AN INTRODUCTION TO THE STUDY OF FOSSILS the parenchyme, and through this parenchyme it is posteriorly closely united with its neighbors. Reproduction. — Each new colony arises from a sexually produced individual. The same zooid possesses both ovary and testis formed from specially modified cells of the paren- chyme. The spermatozoa move about in the coelome and there fertilize the ova. The fertilized ovum passes into a rounded outgrowth of the zooecium, which forms a sort of brood pouch and there develops into the embryo. This escapes from the parent body, becomes fixed by a sucker to some object, and as the " primary zooid " secretes the first cup (protoecium) , and subsequently gives rise asexually by budding to the new adult branching colony. 1. Examine a colony, noting its attachment, method of branching, the individual cups, avicularia. 2. Examine the mounted specimen under a compound micro- scope, noting the U-shaped digestive canal, tentacles surrounding mouth, chitinous cup. 3. What is the habitat of Bugula ? 4. How is it protected ? 5. How does an individual get its food ? 6. Describe the method by which the digested food reaches all parts of the animal. 7. How does it breathe? 8. How are the individuals of a colony united ? 9. Describe its method of reproduction. General Survey of Class Bryozoa Usually colonial and encrusting animals. A tentacle-bear- ing ridge, lophophore, surrounds the mouth. An introvert is usually present, and a U-shaped digestive tube. The two sexes are commonly united in the same individual. The body wall of each individual, called the zocecium, usually becomes hard by means of horny or calcareous materials, forming an exo- skeleton which persists after the death of the animal, and which forms the only portion of the animal capable of being preserved MOLLUSCOIDEA — BRYOZOA 177 in the fossil state. Fossil Bryozoa are known from the Lower Ordovician to the present. Derivation of name. — Bryozoa > Greek bryon, moss, + zoon, animal. The colonies frequently look like tufts of moss. Bryozoa are subdivided into the following sub-classes and orders : — 1. Ectoprocta a. Gymnolaemata b. Phylactolaemata 2. Endoprocta Sub-class i, Ectoprocta Colonial Bryozoa with the mouth inside but the anus out- side the tenacle-bearing lophophore (whence the name from Greek ektos, outside, -{- proktos, the anus). A well-developed introvert is present. Order a, GymjtolcBmata Almost exclusively marine ; lophophore circular ; epistome absent (whence the name from Greek gymnos, naked, + laimoSy the gullet) . At present the marine forms live from tide level to a depth of over 18,000 feet. Geologically they extend from the Lower Ordovician to the present. All fossil Bryozoa known, with possibly a single exception, belong here. Fig. 70. — The marine bryozoon, Membranipora. A, M. pilosa (X 15) from the coast of Massachusetts. Portion of a colony seen from above. B, single cell of same seen in profile. C, same with one of the individual animals expanded as in feeding. D, a fossil species, M. rimulata Ulrich ( X 10), from the Eocene of Maryland. (From Ulrich. A-C from Verrill and Smith.) N 178 AN INTRODUCTION TO THE STUDY OF FOSSILS Membranipora (Fig. 70). Jurassic to present. This genus differs from Bugula in the arrangement of the individuals in the colony. The colony has the form of a fiat expansion incrusting seaweed ; thus the zooecia, the individuals, are arranged in one plane, irregularly, or in rows. Each indi- vidual, as in Bugula, consists of a chitinous bag, but much shorter and with the rim around its aperture calcified. These individual zooecia are united to one another by their thickened walls to form a fiat, net-like framework. 1. Sketch three zooecia of a dried specimen. 2. How many individual animals do these three represent? 3. How do the zooecia differ from those of Bugula ? 4. Of what is the skeleton composed ? 5. Where at present may living Membranipora be found ? 6. What conditions must exist for such a living form to be preserved as a fossil ? Monticulipora (Fig. 71). Ordovician to Silurian. Colonial, occurring as a flat expansion of upright, parallel tubes of calcium carbonate. These tubes have thick, non- cor. tab, Q ^ooK Fig. 71. — Monticulipora arborea Ulrich, from the Middle Ordovician of IMinnesota. A, portion of a colony, natural size. B, view of surface ( X q), showing the cups (corallites, cor.) occupied by the soft bodies of the individual animals during life. C, longitudinal section from the periphery of branch inwards through fifteen corallites (x 18); cor., corallites; tab., tabulae or diaphragms. (From Ulrich.) MOLLUSCOIDEA — BRYOZOA 1 79 porous walls and are divided into compartments by numerous transverse partitions (diaphragms) . The lowest portion of each tube is the narrowest, having been built by the individual in its youth ; from this point the tube rapidly enlarges to its maxi- mum, normal diameter. The diaphragms mark its withdrawal from a lower to a higher position. Unlike Bugula, each tube increases in length throughout life. Since, however, the soft parts of the animal increase in size but little, the lower (older), portions of its house-like skeleton must be vacated ; this removal takes place at more or less regular intervals, probably due to a con- traction of the soft parts of the body following the extrusion of the sexual elements, and w^herever the base of the body comes to rest it secretes a calcareous plate, the diaphragm. The tube openings are polygonal or rounded. The surface of the colony is often made irregularly rough by the elongation of groups of individual tubes so as to form small elevations, — monticules (whence the name from Latin monticulus, sl little hill, + porus, a pore). 1. Sketch (a) outline of entire colony, (b) a view of three zooecia showing both the tubes and their openings, also dia- phragms in one. Label zooecia, diaphragms. 2. What may probably be the cause of the diaphragms? 3. How do the zooecia differ in composition from those of Bugula ? 4. Indicate in one zooecium the position last occupied by the soft portions of the animal. Fenestella (Fig. 72). Silurian to Permian. Colony usually funnel-shaped, composed of a calcareous net-like frame-work made up of straight radiating branches united by cross bars (whence the name from Latin fenestra, a window, -|- the diminutive ending ella). Upon the upper (inner) side of the radiating branches are two rows of small pits (zooecia), separated by a median keel-like ridge ; each of these pits lodged the soft body portion of an individual bryozoon. The cross bars do not bear pits. In development the large first, l8o AN INTRODUCTION TO THE STUDY OF FOSSILS or primary, cup (protcecium) secreted by the sexually produced zooid budded off two cups ; each of these gave rise to others. Continued budding produced the mature colony. Fig. 72. — Fenestella filistriata Ulrich, from the Burlington limestone (Mississippian) of Iowa. A, inner surface of a colony showing the two rows of zooecia. B, outer surf ace of a colony ; note absence of zooecia. Each X 6. (After Ulrich.) 1. Sketch the upper side of a portion of a colony ; indicate the zooecia, median ridge, cross bars. 2. Sketch in outline the probable shape of the entire colony. 3. Outline its development. 4. What is the significance of the name ? Order b, Phylactoloemata Fresh- water inhabitants ; lophophore horseshoe-shaped ; an epistome overhangs the mouth (whence the name from Greek phylassein, to guard, +laimos, the gullet). Unknown in the fossil state, with the possible exception of Plumatellites from the Cretaceous of Bohemia. MOLLUSCOIDEA — BRACHIOPODS l8l Sub-class 2, Endoprocta Colonial or solitary Bryozoa with both mouth and anus within the tentacle-bearing lophophore (whence the name from Greek endon, within, + proktos, the anus). The introvert is but slightly developed or absent. All forms belonging to this small sub-class are marine except the American fresh-water genus Urnatella. Not known in the fossil state. CLASS B, PHORONIDA Marine, worm-like, inclosed in a membranous or leathery tube but unable to withdraw the soft parts of body into it ; a tentacle-bearing lophophore present, very similar to some bryozoan Ectoprocta. Name from Greek Fhoronis, the only living genus. Not known in the fossil state. CLASS C, BRACHIOPODA (BRACHIOPODS) Type of class. — Terebraiulina septentrionalis (living) (Figs. 73 «. ^)- This species is abundant off the coast of Maine, living from low tide to a depth of 300 feet. It occurs from Massachusetts to Nova Scotia inclusive. (Species of the same genus occur in the shallower waters of nearly all seas.) The animal is protected by a calcareous shell, usually five- eighths of an inch long and consisting of two pieces {valves). It is attached to a rock or other support by a posterior, fleshy prolongation of the body, called the pedicle. Skeleton. — The valves are secreted by two fleshy folds of the body, the mantles. The pedicle passes out through a hole (the pedicle opening or delthyrium) in the beak of the larger or ventral valve ; hence this valve is at times called the pedicle valve. Fastened to the inside of the smaller or dorsal valve is a calcareous ribbon-like loop, the brachidium, form- ing an internal support for the hollow, arm-like branches i82 AN INTRODUCTION TO THE STUDY OF FOSSILS (brachia) of the lophophore ; because this valve supports the brachia it is often called the brachial valve. Externally the shell is marked by concentric lines (growth Fig. 73 a. — Terebratidina se ptentrionalis Couthoy, from the coast of Maine. ^, in- side of the brachial valve. B, inside of pedicle valve. C, side view of the animal fastened to a rock by the fleshy pedicle. D, soft body of animal in brachial valve with pedicle valve removed. E, an enlarged section of the brachium along line a-b in figure D, showing the ciliated tentacles {te.) which urge the food into the cili- ated food grooves {f.g.) ; a-b, line of section, Fig. E; a.m., adductor muscle scar; ft., brachial valve ; />r., brachidium ; tra., the horseshoe-shaped lophophore with its branches or arms, — the brachia ; c.p., cardinal process, place for the attach- ment of the diductor muscles ; J.W., diductor muscle scar; J.g., food groove; Ip., lip; mo., mouth; />., pedicle valve; ^e., pedicle; ^e.o., pedicle opening for passage of pedicle; s., socket into which fits the tooth (/.) ; si., sinus; t., tooth ; te., tentacles. All natural size, except E. lines) which represent the successive stages of growth ; as the shell grew new layers were added to the inside, projecting be- yond the preceding layers and forming thus a series of shell ex- tensions. (See also pp. 215, 216.) Since the pedicle is present in the youngest shell-secreting stage of the brachiopod, and the animal when young must have had a minute pedicle, grow^th must MOLLUSCOIDEA — BRACHIOPODS 183 have begun at the small end or beak of the shell. That this was the initial point of growth is seen likewise by the curving of the growth lines around it. The beak, then, is the oldest portion, while the latest built portion is the edge of the shell away from the beak. The pedicle is further inclosed, as it passes out of the valve, by two triangular plates, the deltidial plates, which, therefore, more or less close the delthyrium. A pair of teeth on the pos- terior portion of the pedicle valve fit into corresponding sockets in the brachial valve ; these sockets are also the bases of the calcareous skeleton that supports the arms. Projecting be- tween the teeth of the pedicle valve is a short prolongation, the cardhial process {c.p., Figs. 73 a, 80, 85) of the posterior portion of the brachial valve. Since during the growth of the shell the teeth enlarge externally and anteriorly, while probably both resorption and wear take place internally and posteriorly, the hinge line becomes con- tinually broader ; i.e. the teeth move farther apart and, pari passu, calcium carbonate is added to the inside of the sockets, thus causing the hinge line of this valve likewise to become broader. Thus the brachial valve as a whole moves anteriorly. Muscles. — The valves are opened and closed by muscular action. The pedicle valve may be said to be stationary be- cause to it is firmly attached the pedicle. Two pairs of muscles, the didiictors, extend from^ the posterior portion of the pedicle valves back to the tip of the cardinal process. Being thus situ- ated, their contraction tends to cause the valves to fly open. The valves close by the contraction of two other muscles, the adductors, which pass transversly from valve to valve. These are elongate and narrow on the pedicle valve, and in passing over to the brachial valve divide, leaving here four more or less circular scars. A pair of muscles extending from the brachial valve and another pair from the pedicle valve with insertion on the pedicle enable the animal as a whole to move in many different directions. l84 AN INTRODUCTION TO THE STUDY OF FOSSILS The soft body of the animal, lying at the posterior portion of the shell, occupies only about a third of the interior. The body wall gives off two folds or mantles, one fitting closely to and secreting the pedicle valve, the other secreting the brachial valve. Prolongations of this mantle, the caeca, fitting into minute pores (tubules) in the valves, probably supply nourish- ment to and take waste from the non-calcareous part of the shell. Any marked injury to a mantle is necessarily reflected in the shell. If something injures a mantle edge, the first pro- cess in healing is a puckering up of the mantle around the injured place (as in the healing of an injury to a man's skin) which causes a like puckered appearance in the shell at that place ; as the mantle becomes healed the growth lines of the shell become more and more regularly spaced. But since an injury to one mantle causes a lessened vitality, even if very slight, of the entire animal, the opposite mantle likewise displays a crowding and general interruption of regularity in the growth lines. It thus follows that the life history of the individual can be read from the beak forward, not only in relation to the shape and size of the shell, but to its injuries, social crowdings and general health. (See also Fig. 4.) Most of the inner space between the mantles is filled with the tentacle-bearing lophophore ; this is supported by the calcare- ous ribbon or skeleton, the brachidium. Those portions of the lophophore which diverge arm-like from the two sides of the mouth are called the hrachia. The food consists of diatoms, infusorians, etc., as well as of microscopic organic fragments. Upon each branch of the brachia there is a groove bounded on each side by lines of ciliated tentacles, and which extend from the tip of each arm to the mouth, — a slit-like opening in the middle of the lophophore. The motion of the cilia upon these tentacles and within the food grooves (Fig. 73 a, E) causes a current of water, and with it any near-by food particles, to sweep into the grooves and along these grooves to the mouth. MOLLUSCOIDEA — BRACHIOPODS i8s From the mouth the food passes through an oesophagus into the stomach, into which from each side opens a large stomachal gland which probably performs the functions of both liver and di. . sto. s.g. mo. cm. '"> ■ /I H I Fig. 73 h. — Terebratulina scptentrionalis. F, longitudinal vertical section through entire animal ; G, H, I, young stages of the shell, looking upon the brachial valve and the pedicle opening of the pedicle valve. G, earliest attached stage in the growth of the shell, showing the large open delthyrium. H, a later stage. /, stage showing the introduction of the radiating striae and an approach to the adult in outline, cru., crura (the bases of the brachidium) ; di., diductor muscle; e.g., external glands; mo., mouth; s.g., stomachal glands; sto., stomach. The size of G and H are indicated by the mark within the circle, of / by the line to the right. (From Morse.) pancreas of higher forms, thence into the intestine W'hich ter- minates in a closed point, no anal opening being present (Fig. 73 b, F). The digestive waste, in the shape of minute pear-shaped bodies, is carried out of the stomach through the oesophagus by the cilia lining it, and is ejected through the mouth. The digested food absorbed by the surface of the digestive tract, aided very largely by the stomachal glands, passes into the body cavity surrounding it. The fluid filling this body cavity is moved by the cilia lining it and performs the function of the blood ; thus the digested food entering it is urged into all parts of the body. This body cavity, or ccelome, is continued into the lophophore and its branches ; it also extends into each of the mantle lobes in the form of branched canals, — pallial sinuses; the impression of these upon the shell is often seen in fossil forms (Fig. 85, D, E). The coelomic fluid or blood is colorless and contains corpuscles. A small contractile sac posterior to the stomach has been considered as possibly a heart, and radiating from this are a number of vessels ; since the main blood circula- l86 AN INTRODUCTION TO THE STUDY OF FOSSILS tion, however, is independent of it, its function may be lymphatic or more probably genital. The excretory organs consist of two large funnel-shaped nephridia, one on each side of the intestine. They have a wide inner opening into the ccelome and a narrower outer opening near the mouth ; their function is to get rid of the nitrog- enous waste gathered from the coelomic fluid. Respiration is effected mainly through the mantles, for the blood sinuses branch broadly within them ; it is largely aided also by the lophophore and its tentacles. There is a nerve ring around the oesophagus enlarged into a dorsal and a ventral ganglion which give off nerves to the lopho- phore, mantle, etc. No sense organs are known, but the animal is sensitive to touch. The sexes are probably separate ; at least the same individ- ual does not produce both ova and spermatozoa at the same time. After the fertilization of an ovum by a spermatozoon the single cell divides into two cells. Repeated division results in the formation of a many-celled but hollow^ sphere, — the blas- tula ; one side of this sinks in against the other, producing a two- walled cup, the gastrula. After the cup-like opening of the gastrula closes, the embryo becomes ciliated and is capable of moving freely about. It now becomes gradually constricted into three regions, — the head, thoracic and pedicle areas, with a total length of about a third of a millimeter. From the middle, or thoracic, segment grows a ring-like fold extending back towards the pedicle segment. Soon, however, this cir- cular fold or mantle divides into two, the dorsal and ventral mantle lobes, which develop bundles of chitinous bristles upon their free edges. After three or four days of this early embryonic life, the animal settles down, attaching itself to some foreign object by the end of the mucus-coated, sucker-like pedicle; later the mantle lobes turning inside out, bend forward so as to inclose the head segment and what is now the outer surfaces MOLLUSCOIDEA — BRACHIOPODS 187 secrete the dorsal and the ventral valves of the horn-like, em- bryonic shell {protegulum, Fig. 73 b, G,H,I). About the same time a crescentic fold, the future lophophore, grows out from the inner side of the brachial. mantle lobe, developing gradually into the two arms which diverge from the mouth ; simultaneously the muscles develop, the additions to the shell become calcareous and in all ways the animal approaches the adult. 1. Examine specimens, noting pedicle, mantle, adductor and diductor muscles ; the relation of mouth to food grooves on lophophore. 2. Sketch transverse section of one of the brachia, labeling food groove and tentacles. 3. Make drawings of {a) entire shell, side view, (b) interior and exterior of each valve. Label pedicle and brachial valves, pedicle opening, teeth, sockets, cardinal process, brachidia, adductor and diductor muscle scars. 4. Sketch an ideal longitudinally transverse section through the slightly gaping valves, labeling the valves, pedicle opening, cardinal process, muscles and mantle. 5. How are the valves held together? How are they opened ? How closed ? 6. Give the habitat of Terebratulina septentrionalis. 7. What does the animal eat? How does it procure its food ? 8. Briefly describe its digestion ; absorption ; circulation. 9. How is the digestive waste thrown off ? 10. How does the animal breathe ? 1 1 . What is its nervous system like ? 12. Describe the development of an individual from the fer- tilized egg to adulthood. General Survey of Class Brachiopoda Marine animals, secreting a bivalved, equilateral, inequivalved shell, which is composed of lime carbonate, lime phosphate, or a horny substance (ceratin) ; the valves are dorsal and ventral in position. The animal, in its youth, is always attached to a foreign object by a posterior, fleshy stalk, called the pedicle; 1 88 AN INTRODUCTION TO THE STUDY OF FOSSILS when adult the pedicle may be lost, but in all such cases the animals are held in place by social crowding, spines, or other devices (Rafinesquina, Stropheodonta demissa, Productus) ; at times it is cemented to some foreign object (Crania, Meekella, Richthofenia). ie. f U/77A a y^^^^f?^ del. Z7// \ — ■ '^o^ J^^lk^ /?/ C ^ Fig. 74. — Spirifer increbescens Hall, from the Mississippian of Alberta, (x 2.) a-b, length of shell (from hinge line beneath the beak to front of shell) ; b, anterior margin or front of shell; be., beak, the posterior end of the shell; bv., brachial valve ; c-c', width of shell ; c and c' are the cardinal extremities ; ca., cardinal area of pedicle valve, the flattened area above the hinge line and between the cardinal extremities (each valve has a cardinal area) ; d-e, height of shell (measured between the centers of the valves and at right angles to the plane of length and breadth) ; del., delthyrium, or triangular pedicle opening ; gr.l., concentric growth lines marking the anterior margin of the shell at successive periods ; h-h', hinge line (compare Fig. 78, hi.) ; m.f., median fold (composed here of four plications in this species) ; pi., plications (folds radiating from the beak, not longitudinally striate) ; p.v., pedicle valve ; umb., urnbo of pedicle valve. For terms describing the exterior of the shell see Fig. 74. The valves are opened and closed by muscles, the impressions of which show upon the interior of the valves in front of the beaks (Fig. 73 a). For formation of ribs, etc., see p. 220. The interior of the shell is lined by the mantle, — a mem- branous fold of the body- wall, which is often studded with minute tubes, the caeca ; these fit into correspondingly mi- nute holes (tubules) in the shell ; the tubules give to the shells MOLLUSCOIDEA — BRACHIOPODS 1 89 their punctate appearance ; in some species, as Terebratella plicata, this is quite coarse, being almost visible to the naked eye. Within the mantle are hollow spaces, the pallial sinuses ; impressions of these sinuses are often found upon the interior of the valves. The pedicle valve is secreted by the ventral and the brachial valve by the dorsal mantle lobe. In those forms in which the brachial valve as a whole moves forward during the enlarge- ment of the shell this would leave the dorsal surface of the pedicle unprotected were it not that this surface has developed upon it one or two special plates. In a portion of the Articulata (the Protremata) the surface of the pedicle itself secretes a shell, — the deltidium, which unites with the posterior margin of the pedicle valve and continues to grow anteriorly (as in Rafines- quina). In the rest of the Articulata (Telotremata) where the deltidium is absent, the extension of the ventral mantle lobe grows out laterally for the protection of that portion of the pedicle by a secretion of two plates, — the deltidial plates (as in Atrypa) . Teeth and sockets are absent in many forms with ceratin (horn-like) shells ; these are therefore known as thelnarticulata, the opening and closing of the valves being effected by a more complicated set of muscles. In the great majority of brachio- pods the shells are calcareous and here there are teeth and sock- ets ; these are the Articulata. In the Inarticulata, where the setae upon the mantle margins are long, acting as strainers (Fig. 75) to the ingoing water, the shells are non-plicate. In the Articulata, where the setae are short, the shells are often plicate. In a plicate shell the valves need open but slightly to admit sufficient water and yet keep out sand, enemies and other objectionable objects. The pedicle valve can usually be distinguished from the brachial by some one of the following characters : 1. Larger size and greater depth. 2. Presence of a pedicle opening. igo AN INTRODUCTION TO THE STUDY OF FOSSILS 3. Higher cardinal area (vertical distance from hinge line to beak) than in the brachial valve. 4. Beak incurved over that of brachial valve. Brachiopod shells often appear to be very similar to pelecy- pod shells, but may usually be readily distinguished from them by one or more of the following characters : I. 2. 3- Brachlopoda Equilateral Inequivalved Pedicle opening present (ex- cept in Atremata) 4. Teeth in one valve, sockets in the opposite valve (except in Inarticulata) 5. No ligament present ; valves opened by muscles 6. Valves dorsal and ventral Pelecypoda 1. Inequilateral 2. Equivalved (generally) 3. No pedicle opening present (in some a byssal notch or hole) 4. Teeth and sockets in each valve (typically) 5. Valves not opened by mus- cles but by ligament or resilium at hinge line 6. Valves right and left It is suggestive of retrogression in the Articulata sub-class that while in living species the anus ends blindly, in Paleozoic forms it was probably functional. In Rensselaeria, Athyris, Atrypa, Rhynchonella, etc., the beak of the brachial valve is notched or perforate (between floor of valve and union of the bases of the arm supports) for its passage to the exterior. In Strophomena and Stropheodonta it passed between the branches of the cardinal process. In living Inarticulata, as Lingula, the digestive canal ends in an open anus. All brachiopods are in the larval stage free-swimming, sometimes for a very short time (longest among Inarticulata) ; it is hence during this period that their distribution in space takes place. The cause of the distribution is mainly one of ocean currents, since the microscopic larva, about a third of a millimeter long, swims about by a twirling motion for compara- tively few hours and at a rate which could carry it only about a yard an hour. MOLLUSCOIDEA — BRACHIOPODS 1 9 1 Brachiopod shells are small, averaging from a half inch in length and breadth to an inch and a half. The largest species known — Prodiictus giganteus of the Mississippian — reaches at times a width of almost a foot, while mature forms are known which are no larger than a pinhead. There are about 160 species of living brachiopods, which are distributed in ^t^ genera. Over 75 per cent of these species belong to the Articulata. Living brachiopods are found in all seas and down to depths of 17,000 feet, hence at all oceanic temperatures ; about 20 per cent live in the shallow seas around Japan, the most prolific area for these shells. Over 70 per cent live in shallow waters, i.e. from between tides to a depth of 600 feet. The great ma- jority (75 per cent) of the Inarticulata live above the 15-fathom line, while but 20 per cent of the Articulata live here. Com- pared with the deep sea species, the shallow water and littoral forms are much more prolific in numbers, with much thicker and usually larger shells. Brachiopods are thus very important in the study of ancient geography. For example, the presence of fossil Inarticulata, especially those of the Lingula group, is good evidence of shallow water deposits. Of those species be- longing to groups existent in the Paleozoic not one is known which at present has a wholly abyssal habitat ; most of the abyssal forms date from stocks having their rise in the mid- dle Mesozoic or later. Hence the conclusion, corroborated by other classes of animals, that abyssal seas began to form at the close of the Paleozoic with the late Paleozoic upheavals, known for North America as the Appalachian Revolution. Though all brachiopods are strictly marine in habitat, some forms, such as Lingula, can endure a considerable amount of fresh, water, living in estuaries where there are heavy spring freshets, but they never live in rivers. The living inarticulate brachiopods possess a wonderful vital- ity. Lingula may be exposed between tides, covered with mud from freshets, or immersed in fetid water for months without 192 AN INTRODUCTION TO THE STUDY OF FOSSILS apparent ill effects. Crania will also thrive under most adverse conditions. Such adaptability is probably the cause of the persistence of these two genera from Ordovician times to the present. The persistence of genera and species in time varies greatly. Some genera, as Hipparionyx and Rensselaeria (Lower Devo- nian), survived but a short time ; while others, as Lingula and Crania, have existed since Ordovician times. Rhynchotrema capax (Richmond formation of the Upper Ordovician), for ex- ample, was short-lived but of wide distribution ; it is thus a good index fossil (see page 22), while Leptcena rhomboidalis, persisting from mid-Ordovician to Mississippian, A try pa retic- ularis, throughout the Silurian and Devonian, and Productus semireticulatus, throughout the Mississippian and Pennsylvanian, were the brachiopod Methuselahs of the Paleozoic ; these forms are accordingly almost valueless as indicators of the age of their inclosing strata. Brachiopods are known since the earliest Cambrian, and therefore the class must have originated in the pre-Cambrian ; the class reaches its maximum of differentiation in the Silurian and Devonian, with the dying out of stocks in the late Paleo- zoic. Since Mesozoic times the rhynchonellids and terebratu- lids have dominated, and along with them a few lingulids, dis- cinids, cranids and strophomenids have persisted. The class is tending slowly toward extinction. Derivation of name : Brachiopoda > Greek brachion, arm, + pous (pod), foot. The arms (brachia) were formerly thought to be organs of locomotion. The Brachiopoda are subdivided into two sub-classes : 1. Inarticulata. 2. Articulata. Sub-Class i, Inarticulata Valves held in apposition merely by muscles, there being usually no teeth or sockets to hold the two valves firmly together MOLLUSCOIDEA — BRACHIOPODS 193 (whence the name from Latin in, not, + articulatus, jointed). Intestine ends in an anus ; this in the Lingula group opens laterally between the two valves. Lingula (Fig. 75). Basal Ordovician to present. Valves thin, almost equal, elongate, tapering towards the beak {i.e. tongue-shaped, whence the name from Latin lingula, f af ^SXO A B Fig. 75. — Brachiopod movements. A, a Lingula-like shell, Glottidia pyramidata, very abundant upon the shoals of the North Carolina coast, ixposed at low tide. Natural size. i. A characteristic attitude; the sand tube inclosing the pos- terior end of the pedicle is here preserved. 2. Faeces (/.) being extruded from shell. B, Lingula lepidula, very abundant upon the coast of Japan, showing the formation of tubes by the mantle and setce. Through these tubes the water is urged by the cilia lining the brachia, and with the water food is taken in and waste is extruded by the outgoing current. 3. Attitude in sand with setal tubes formed; the brachia show through the transparent shell. 4. Front view of above, a./., anterior folds of mantle ; br., brachia ; s., surface of the sand in which the animal lies half buried. (From Morse.) a little tongue). Valves glistening, composed of alternate layers of phosphate of lime and a horn-like substance (ceratin), im- punctate. The animal burrows in the sand by means of the long, slender pedicle which emerges from between the two valves and 9 194 AN INTRODUCTION TO THE STUDY OF FOSSILS not through one of the beaks as in the majority of other brachiopods. Lingula anatina is a large species very abundant in the Japa- nese seas. Glottidia pyramidata (Fig. 75, A), belonging to the Lingula group, is very abundant off North Carolina on shoals exposed at low tide ; it occurs from Chesapeake Bay to Florida. In its normal condition, it lies with its shell half buried in the sand, its anterior setae so grouped as to form three rude channels for the entrance of water at the angles of the front of the shell and for its exit at the middle. Each mantle is at the same time raised into two folds, one upon each side of the median line of the shell, thus aiding in the formation of these water channels (see Fig. 75, B). The tentacles of the brachia are directed towards these setal tubes, while the vigorous motion of the cilia covering the tentacles causes the movement of the water. At this time the two valves are separated vertically but not laterally. Anteriorly they are open, but posteriorly as nearly closed as the pedicle will allow. The sand is kept out of the buried portion of the shell by the arrangement of the lateral setae vertical to the plane of the valves, the setae from opposite mantles meeting tip to tip. When disturbed the shell is quickly drawn down into the sand through the contraction of its long pedicle, the lower end of which obtains greater purchase by being sheathed in a tube of sand grains cemented together by the mucus which it secretes. This species does not live beyond a year. 1. Examiae specimens on the demonstration table, noting the elongate pedicle emerging from between the two valves. 2. How long geologically has Lingula existed? 3. Is either valve perforated by a pedicle opening ? 4. What is the use of the long pedicle ? 5. How does the animal get its food? 6. What is the composition of its shell ? 7. How do fossil Lingulae indicate the depth at which the inclosing sediment accumulated ? MOLLUSCOIDEA — BRACHIOPODS 195 Crania (Fig. 76). Ordovician to present. Shell small, nearly circular in outline, without pedicle open- ing in adult but cemented by apex or by entire surface of pedicle valve to the surface of a shell or other foreign object. Brachial (upper) valve conical, with beak almost central and directed pos- teriorly. In each valve there is a pair of widely separated muscle scars near the posterior margin and a pair close together near the center. Impressions of the pallial sinuses branch iinger-like. I. Sketch a valve, naming the valve and noting muscle scars if present. Sub-class 2, Articulata IiG. 76. — Crania bordeni Hali and Whitfield, from the Middle De- vonian of Indiana. Natural size. A, an entire individual attached to a brachiopod shell which has vertical ribbing at the right of the figure. The conformation of the upper valve to the ornamen- tation of the brachiopod shell in- dicates the intimate relationship existing between the mantle edges of the two valves. B, side view of the same. (After Hall and Clarke.) Valves held firmly together by teeth and sockets (whence the name from Latin articulatus, jointed). In living species the intestine ends blindly, but in some Paleozoic forms it apparently opened through a foramen in the cardinal area of the brachial valve ; if this opening was in life occupied by the anus, it suggests that a degeneration in structure has accompanied the retrogression in numbers for this sub-class. Rafiaesquina (Fig. 77, A, B). Almost wholly Ordovician. Pedicle valve more or less convex, often without pedicle opening in the adult. The apex of its beak has a minute de- pression, — the pedicle opening of the very young shell, — but with age the pedicle usually disappeared, probably through resorption. The shell rested free upon the sea-bottom, but was held in place through social crowding, while the inner end of the pedicle opening became filled with lime, secreted prob- 196 AN INTRODUCTION TO THE STUDY OF FOSSILS ably by the extension of the ventral mantle. Brachial valve flat or concave. Hinge line straight. Surface with radiating pdm. Fig. 77. — Rafinesquina alternata Conrad (X f), from the Ordovician of Cincin- nati, Ohio, yl, exterior of brachial valve. 5, exterior of pedicle valve. C, inte- rior of pedicle valve of Strophomena. a.m., adductor muscle scar; a.d.m., pos- terior diductor muscle scar; delt., deltidium ; p.d.m., anterior diductor muscle scar; t., tooth. (From Hall and Clarke.) striae alternating in size. Shell punctate. (Name in honor of the French-American scientist, Rafinesque.) R. alternata is the most widely spread and abundant species, being found almost everywhere in the Middle to Upper Ordo- vician of North America. 1. Sketch (a) exterior of pedicle valve, (b) cardinal areas of entire shell, (c) the cut portion of a vertical section through entire shell from beak forward. Label in all, where present, pedicle and brachial valves, hinge line, cardinal areas, beak, deltidium, front of shell. 2. Indicate in sketch i (a) the oldest portion of shell, stating your reasons. 3. How do you know the convex valve is the pedicle valve ? 4. Draw in your sketch of the pedicle valve the outline of the shell when half grown, stating how you know that this was its shape. 5. State whether the animal was attached or free when adult, giving reasons. Strophomena (Figs. 77, C, 78). Ordovician. A resupinate Rafinesquina, i.e. pedicle valve concave or sigmoid in section, and the brachial convex. The muscular area on the pedicle valve is sharply limited by elevated ridges. Shell punctate. MOLLUSCOIDEA — BRACHIOPODS 197 1. Sketch the cut portion of a vertical sec- tion through the entire shell from beak for- ward, labeling the pedicle and brachial valves. 2. How do you distinguish this genus from Rafinesquina ? 3. Was the pedicle valve concave and the brachial conv^ex in its youth as it is in its adult state ? Reasons. Leptaena (Fig. 79). Ordov ic i an- Miss iss ipp ian . Pedicle valve convex, brachial concave. The flat portion of the shell is concentrically wrinkled; where these wTinkles cease the shell is abruptly deflected. Shell with closely appressed valves, thin, i.e. with \'ery little space for the soft parts of the animal. Shell punctate. I. Sketch {a) a view of exterior of pedicle valve showing the concentric wrinkles and the deflected anterior portion, (h) the cut portion of a vertical section through the entire shell from beak forward. Note pedicle and brachial valves. Fig. 78. — A diagram- matic longitudinal cross section of the brachiopod shell. Strophomena pla- numbona Hall ( X 2). Section cut beside the deltidium. This is similar to Rafines- quina (Fig. 77), ex- cept that the con- vexity of the valves is reversed •,b., brachial valve ; c.a., cardi- nal areas of brachial and pedicle valves ; //./., hinge line; p., pedicle vah^e. pe.o. A B C Fig. 79. — Leptcena rhomboidalis Wilckens. A, aduh brachial valve (natural size), showing the exceptional retention of the pedicle opening {pe.o.) in the opposite (pedicle) valve. B, adult pedicle valve. C, pedicle valve ( X lo), a young stage in the growth of the shell showing the beginning of the radiating striae. C redrawn from Beecher. {A and B after Hall and Clarke.) 198 AN INTRODUCTION TO THE STUDY OF FOSSILS Stropheodonta (Fig. 80). Silurian to Devonian. Shell similar to the preceding but with the hinge margins marked by more or less long transverse ridges which terminate in teeth that articulate as teeth and sockets (whence the name from Greek stropkis, a band, + odous, a tooth, a band of teeth). Shell punctate. a.a.m. p. am. Fig. 80. — Stropheodonta concava Hall, from the Hamilton (De- vonian) of New York. ( X f .) Muscle area of the interior of a brachial valve, a. a.m., the broad posterior adductor mus- cle scars; c.p., cardinal pro- cess for attachment of di- ductor muscle; gr., vertical grooving, or ridging, of the edge of shell at hinge line, giving rise to the name ; p.a.m., the elongate anterior adductor muscle scar. (From Hall and Clarke.) 1. Sketch (a) exterior of pedicle valve, (b) cardinal areas of entire shell. Label valves, deltidium, transverse ridges. 2. How do you distinguish this genus from Rafinesquina ? times produced into ears. Productus (Fig. 81). Devonian to Permian. Shell free, or anchored in the mud by the tubular spines growing from the convex pedicle valve. Brachial valve concave, spinose or lamellose. Hinge line not well developed, some- Entire surface marked with radiating ribs, or elongate pustules, which are usually studded with spines. Shell punctate. (Name from Latin productus, produced ; so named from the prolongation of the beak of the pedicle valve beyond that of the brachial.) Productus semireticulatus is world-wide in distribution, in the Mississippian and Pennsylvanian. 1. Looking fully upon the hinge line of entire shell, sketch a view showing brachial valve and umbo of pedicle valve ; indicate valves, spines, radiating ribs. 2. State whether the animal was attached or free when adult, giving reasons. 3. How were the spines formed? 4. Is Productus semireticulatus a good index fossil ? Reasons. MOLLUSCOIDEA — BRACHIOPODS 199 Fig. 81. — Prodiictus semireticidatus Martin, from the Pennsylvanian of Indiana. Three views of one individual, natural size. A, pedicle valve; B, brachial valve with umbo of pedicle valve showing over edge of hinge line. C, side view. (After White.) Platystrophia (Fig. 82). Ordovician to Silurian. Hinge line long. Both valves very convex, with a strong median fold in the brachial valve and a corresponding deep sinus in the pedicle valve. Entire surface covered with broad, strong, sharp plications (whence the name from Greek platys, wide, -\- strophos, a band). Shell impunctate but with a granu- lose surface. 200 AN INTRODUCTION TO THE STUDY OF FOSSILS This has developed from Or this lenticular is of the Upper Cambrian, a phcate species with a smooth median fold upon the pedicle valve and a smooth sinus upon the brachial. Later the median fold of the former becomes depressed between the two bounding plications forming the central plication of the median Fig. 82. — Platystrophia lynx (Eichwald), from the Upper Cincinnatian of Indiana. a, surface of pedicle valve, natural size ; a', junction of the two valves anteriorly ; a", junction of the valves posteriorly, showing the open delthyrium ; b, exterior of pedicle valve of a very young individual, showing the introduction of plica- tions; b', posterior view of same; b.v., brachial valve; p.v., pedicle valve. The natural size of V is noted by the black spot to the right. (From Cumings, who has worked out the recapitulation of Platystrophia.) sinus of the adult shell, while the two plications bounding the early median sinus upon the brachial valve become, through their enlargement, two of the plications of the strong median fold of the adult. This shifting of the median sinus from brachial to pedicle valve may be due to the enlargement of the median lobe of the brachia, thus keeping the mantle from sagging here. All species of Platystrophia, whether from the Ordovician or Silurian, pass through the same Orthis lenticularis stage (shown at the beak in well-preserved specimens). Platystrophia looks much like Spirifer, but has no calcareous supports for its brachia, and the cardinal area of the brachial valve is almost as high as that of the pedicle valve. Platystrophia lynx is a very abundant species from the Lor- raine (mid-Ordovician) of the Appalachian region and of the Ohio Valley. MOLLUSCOIDEA — BRACHIOPODS 20I 1. Sketch (a) side view of entire shell, (b) view looking fully upon hinge line. Label in each the valves, cardinal areas, plica- tions. 2. Describe as much of the evolution of Platystrophia, noted above, as is preserved upon the specimens at hand. What can you say as to its probable ancestry ? 4. What is the significance of the name ? Fig. 83. — Rhynchotrema capax (Conrad), from the Upper Ordovician of Indiana. Natural size. A, side view of the joined valve; b., brachial valve; p., pedicle valve. B, brachial valve with beak of pedicle valve showing above. C, pedicle valve showing the deep median depression. (From Indiana Survey.) Rhynchotrema (Fig. '^t,). Ordovician. Valves thick, very convex. Pedicle valve strongly incurved at umbo, with thick concave deltidial plates. Entire surface covered with strong, radiating plications crossed by many con- centric growth lines. (Name from Greek rhynchos, a beak, + trema, a hole ; the forms usually have the beak of the pedicle valve perforated by a pedicle opening.) R. capax was widely distributed throughout the shallow ocean covering much of North America during Upper Ordovician time. In some adults a large pedicle opening is present, in others it is absent. 1. Sketch (a) side view of entire shell, (b) anterior view, (c) cut portion of a vertical section through entire shell from beaks forward. Label valves, plications, growth lines, mnbos. 2. Was this specimen attached or free when adult ? Reasons. 3. By means of an ideal sketch, explain how the shell was built ; what do the growth lines represent ? 202 AN INTRODUCTION TO THE STUDY OF FOSSILS 4. In sketch i (c) indicate by drawing in the muscles how the valves were opened and closed. 5. How do brachiopods eat? Breathe? 6. Do brachiopods live in the sea or in fresh waters ? 7. At what depths do they live? Terebratula-like forms (Fig. 84). Devonian to present. Shell usually biconvex, and elongate oval. Pedicle valve has generally a large circular pedicle opening (whence the name from the Latin diminutive of terebratus, perforated). Deltid- ial plates prominent. The old genus Terebratula has been sub- divided into many genera. Rensselaeria is an ancient type from the lower Devonian of North America and Europe. Terebratula harlani is a large form abundant in the Cretaceous of the Atlantic coast of North America, where also is the coarsely punctate species Terebratella plicata. For Terebratulina septentrionalis see page 181. Note the large pedicle opening, deltidial plates and micro- scopic punctae of T. harlani, the coarse punctae of T. plicata. Atrypa (Fig. 85). Silurian to top of Devonian. Pedicle valve slightly convex, brachial usually very convex. Entire surface radially plicate, crossed by many more or less prominent concentric lamellae of growth. Apices of spiral bra- chidia directed towards middle of brachial valve, hence the strong convexity of this valve. Atrypa reticularis is very abundant throughout the world in the Silurian and Devonian. The Silurian forms are usually smaller with brachial valves much less convex and with less ex- tensive lamellae than the Devonian forms. Fig. 84. — Terebratula harlani Mor- ton from the Cretaceous of New Jersey. A, brachial valve, with pedicle opening (ped.o.) of oppo- site valve showing above. B, surface of pedicle valve. ( X 2-) (After Whitfield.) MOLLUSCOIDEA — BRACHIOPODS 203 Fig. 85. — A try pa reticularis Linne, from the Hamilton formation (Middle Devo- nian) of New York. Natural size. .4, side view showing both valves. 5, brachial valve. C, interior of brachial valve. D, interior of pedicle valve. E, mantle of the living Terebratulina coreanica with the sinuses (spaces in the mantle cavity) filled with eggs. The eggs have not been indicated in the mantle of the pedicle valve. Beneath these sinuses roughened thickenings of the shell fre- quently occur, especially in the old shells as at of figure D. a.m., adductor muscle scar (in figure C it includes all the scars within the shell) ; b., brachial valve; c.p., cardinal process; d.m., diductor muscle scar; la., lacuna; m.p., main paUial sinus; 0., ovarian markings on shell; p., pedicle valve; p.c, cavity for attachment of pedicle; s., socket; /., tooth. {A to D after Hall and Clarke; E after Morse.) 1. Sketch {a) exterior of pedicle valve, {h) exterior of brachial valve with umbo of pedicle valve showing, (c) interior of pedicle valve. Label valves, plications, growth lines, impressions of pallial sinuses, adductor and diductor muscle impressions. 2. What function did the pallial sinuses perform? 3. How were the growth lamellae formed? Illustrate by sketch. Spirifer (Figs. 74, 86). Silurian to Permian. Shell usually wider than long, with straight hinge line. Pedi- cle valve usually with high cardinal area and strong median 204 AN INTRODUCTION TO THE STUDY OF FOSSILS tiG. 86. — Spirifer mucronatus Conrad, from the Hamilton (mid-Devonian) of New York, show- ing the long, tapering spirals attached to the inside of the brachial valve for the support of the brachia. Natural size. (After Hall and Clarke.) sinus. Brachial valve with very low cardinal area and strong median fold. Surface of entire shell radially plicate or striate, or with the fold and sinus not plicate, crossed by more or less strong growth lines. Brachidia are spirals (whence the name, from Latin spira, a spire, + ferre, to bear) ; the spirals are directed towards the cardinal angles (hence the great width of the shell) ; some Spirifers have spirals of 35 rev- olutions. The animal was anchored by a short pedicle which passed out through the delthyrium. The genus Spirifer of authors has been sub- divided into many genera made necessary by the variations in the vast number of species found. S. mucronatus is a characteristic Middle to Upper Devonian species of North America ; S. disjunctus, an Upper Devonian species throughout North America and most of the world ; S. cameratus, a widely distributed North American Pennsylvanian species. 1. Sketch (a) side view of entire shell, (b) exterior of pedicle valve, (c) view looking directly upon the hinge line, (d) interior of brachial valve showing the spirals. Indicate in sketches the valves, plications, growth lines, median sinus, median fold, hinge line, cardinal areas, delthyrium, spirals. 2. What is the relation of the mantle to the shell ? 3. What was the function of the spirals ? 4. How do you distinguish this genus externally from Platy- strophia ? 5. What is the significance of the name Spirifer ? 6. What is the geologic range of the class Brachiopoda ? 7. During what periods did the greatest number of brachiopods live? 8. How many species are living at present ? MOLLUSCOIDEA — BRACHIOPODS 205 1. Define each of the classes into which the MoUuscoidea are divided, giving a recent and fossil example of each where possible. 2. Which class has the best-known fossil representatives? 3. What do Bryozoa and Brachiopoda possess in common that they should be placed in the same phylum ? 4. Do these two classes enter into direct competition as regards food getting ? 5. How do the MoUuscoidea differ from the Coelenterata in the following characters : (a) habitat, {h) protecting and sup- porting skeleton, (c) locomotion, (d) food, {e) its capture, (/) its intake, (g) digestion, (h) blood circulation, {i) excretion of waste, (/) respiration, (k) nervous system, (/) sense organs, {m) repro- duction, (n) geologic range ? 6. How do the MoUuscoidea differ from the Annulata in the characters given under question 5 above ? PHYLUM X, MOLLUSCA (MOLLUSKS) The Mollusca as a group possess bilaterally symmetrical, unsegmented bodies enveloped in a sac-like fold, the mantle, which secretes a protective exoskeleton, the shell. The primi- tive bilateral symmetry is often obscured by a secondary torsion of the body. They are mostly free-living, able to crawl, swim and burrow. The general external divisions of the body are the head (ab- sent in the Pelecypoda), — possessing mouth, various kinds of appendages, and nearly all the organs of special sense ; the foot, — a ventral projection of various shapes ; and a dorsal portion, — including the viscera and covered by the mantle which se- cretes a shell. The digestive system consists of three divisions : (a) an anterior division, consisting of the mouth, buccal cavity (absent in most pelecypods) and oesophagus ; the buccal cavity con- tains the characteristic radula ; (b) a middle division, — the stomach, into which pours the secretion of the liver, an im- portant digestive gland ; (c) a posterior division, — the in- testine, ending in an anus. The circulatory system consists largely of closed tubes, al- though there are some open sinuses. It includes a heart con- sisting of one ventricle and usually two auricles (in Nautilus, four) . The blood is a fluid with both nutritive and respiratory func- tion. It varies in color among different moUusks, being colorless, bluish from the presence of hsemocyanin, or red from the pres- ence of haemoglobin. Respiration is usually effected by ctenidia or gills, — spe- cialized expansions of the ventral surface of the mantle, through 206 MOLLUSCA — CHITONS 207 which passes nearly all of the blood just before entering the auricles on its way back from circulation throughout the body. The excretory system consists primarily of renal sacs or kid- neys, — tubes which in most mollusks connect the body cavity with the exterior through the mantle cavity. Nearly all of the venous blood traverses the kidneys on its way to the gills and is by them purified of the nitrogenous waste products of metabolism. The nervous system consists essentially of a nerve ring sur- rounding the oesophagus, giving off four nerve cords, — a pair to the dorsal region of the body and a pair to the ventral region. The sexes are usually separate. The union of spermatozoa and ova is followed by laying of eggs, usually in a gelatinous or leathery matrix. Most mollusks (Cephalopoda excepted) in their development pass through a larval stage, the veliger, in which the tiny, free- swimming form possesses a thickened retractile rim in front of the mouth, which bears a circlet of cilia and is called the velum. A shell gland on the dorsal surface secretes the shell, character- istic of most Mollusca. Derivation of name. — Latin molluscum, a soft-bodied animal. The Mollusca are divided into the following classes ; the names are mainly references to the form assumed by the foot : Page A. Amphineura 207 B. Pelecypoda . , 208 C. Gastropoda 234 D. Scaphopoda 250 E. Cephalopoda 251 CLASS A, AMPHINEURA (CHITONS) The Amphineura are distinguished by their bilaterally sym- metrical body, with mouth and anus at opposite ends. They possess a foot adapted for creeping. The mantle surrounds 2o8 AN INTRODUCTION TO THE STUDY OF FOSSILS the body either entirely (in the Aplacophora) or only dorsally (in the Polyplacophora), and secretes in the former order cal- careous spicules, in the latter a dorsal armor of eight plates. Amphineura are marine, in all oceans, with a wide range in depth. They have existed since Ordovician times. All fossil forms are members of the Polyplacophora, — those possessing a dorsal armor (Fig. 87). Fig. 87. — Dorsal view „ _ of a living chiton CLASS B, PELECYPODA cuiata Carpenter) ^ypc of class, Veuus merceuarta (Figs. from Massachusetts 88— Ql). (but abundant from tt- • n i • i ^i Cape Cod to Flor- Venus mercenaria, called variously the ida). (From Verrill hard or little-ncck clam or quahog, is a and Smith.) . j. . . , r . . warm water lorm with range oi greatest abundance along the southern Atlantic coast from the southern side of Cape Cod to Texas. North of Cape Cod it occasionally occurs up to the Gulf of St. Lawrence. It is found most abun- dantly on sandy and muddy flats just below low water mark, but its possible range is great, from high tide line to a depth of over 50 feet. It burrows into the mud to a depth just sufficient to cover the shell. This species has inhabited the Atlantic coast since Miocene time. The soft body (Fig. 88, B) is inclosed in a calcareous shell which consists of two halves, the valves, joined by a hinge along the dorsal edge. From one end of the ventral or open edge of the shell protrudes a muscular, tongue-like body, the foot, by means of which the animal may slowly make its way through the sand or mud, in which it lies superficially buried. The presence of the foot indicates that end to be anterior and it is in that direction that the animal moves. From the opposite, the posterior end of the shell, project two tubes, the siphons, united almost to their ends. When the valves are opened, each is found to be lined by a thin membrane, the mantle. MOLLUSCA — PELECYPODS 209 The two lobes of the mantle are attached to the body dorsally, and extending down over the sides, come closely together along Fig. 88. — The quahog, Venus mercenaria Linne, in position of feeding. (X f.) Left valve separated from its mantle and muscles which are left lying in the right valve, a.a., anterior adductor muscle and scar; a.r., anterior retractor muscle (a portion of it is attached to the left valve) ; c.t., cardinal teeth ; e.s., excurrent siphon ; i.s., incurrent siphon ; /., ligament ; /./., lateral teeth ; m.m., mantle muscle; p.a., posterior adductor muscle and scar; p.l., pallial line (the scar left by the mantle muscle); />./■., posterior retractor muscle and scar; ^.5., pallial sinus (the scar left by the siphonal muscle) ; s.m., siphonal muscle. the ventral edge, thus inclosing the body of the animal as in a sac. The siphons are merely projections of the mantle edge united into muscular tubes. The lower is the incurrent or branchial siphon ; it draws in water carrying food to the mouth and oxygen to the gills. The upper is the excurrent or anal siphon ; it discharges the waste products of the digestive system and the water which has passed over the gills and has hence become impure with the products of respiration. The organs of respiration are the gills and mantle. The gills are two thin, curtain-like folds hanging free on each side of the main body mass just beneath the mantle (Fig. 89, B). Each 2IO AN INTRODUCTION TO THE STUDY OF FOSSILS of these four gills is double, being a very narrow bag open dor- sally. From the union of these gills with each other and with the mantle on each side, and anteriorly with the viscero-pedal mass (the main body mass into which the foot merges), it results Fig. 89. — -Vertical section through the qxiahog, -Venus mercenaria Linne. A, looking into the shell toward the anterior end. a.a., anterior adductor muscle; a.r., anterior retractor muscle scar; I., ligament showing its C-spring shape; //., left valve; rt., right valve; s., section of shell showing the increments of growth. B, an ideal section through a pelecypod. Such a section may be com- pared to a book, with binding along the dorsal (ligamental) edge and with the valves corresponding to the covers, the mantle lobes to the fly leaves, the two pairs of gills to the first two and the last two pages and the foot to the remainder of the leaves fastened together. that the gills form a partition extending through the mantle cavity, dividing it thus into two chambers. Of these the upper is called the cloacal and from it passes the exhalant or anal siphon ; the lower is called the branchial and into it opens the inhalant or branchial siphon (Fig. 90) . The gills are vertically striated. Microscopic examination shows these striae to be parallel hollow tubes. Thus it is seen that each lamellar half of a gill is composed of a series of these MOLLUSCA — PELECYPODS 211 tubes placed side by side and bound together. Through them the blood circulates and their walls are bathed on all sides by the water which pours into the gills between the tubes. As these walls consist of a single layer of cells, there is a ready inter- change between them of the waste gases (which the blood brings from the body to the gills) and the oxygen of the water. Fig. 90. — The quahog, Venus mercenaria Linne, in position for feeding (natural size), partly dissected lying in the right valve; a., anus; a.a., anterior adductor muscle; a. r., anterior retractor muscle; e.5.,excurrent siphon; g/., cut edges of gills; h., heart ; i.s., incurrent siphon ; /., ligament ; li., liver ; ma., mantle cut and pinned back to show the organs within its cavity ; mo., mouth ; pa., palps or lips at side of mouth ; p. a., posterior adductor muscle ; p.r., posterior retractor muscle. 212 AN INTRODUCTION TO THE STUDY OF FOSSILS Water, admitted through the branchial siphon into the branchial chamber of the mantle cavity, is driven in a rapid continuous current into the gills by the cilia bordering them. From the gills the water passes in a strong current into the cloacal chamber and thence through the exhalant siphon to the exterior. The mantle likewise functions in respiration, being a thin-walled reservoir for blood in contact with the water. Food as well as oxygen is brought to the animal in the water introduced by the branchial siphon into the mantle cavity. The principal food is diatoms, though according to the location and the season the clam feeds also on small crustaceans and rotifers, protozoons and larvae of mollusks. These small food particles are swept in with the current and become en- tangled in the mucus poured out by the gland cells of the gills. Movements of the cilia on the gills urge these food masses on to the mouth. This lies in the median line just below the an- terior adductor muscle. Triangular flaps, the labial palps, unite above and below it to form an upper and a lower lip. The food is swept by the cilia on these palps into the mouth and thence passes through the oesophagus into the stomach. Here it is digested by the fluid poured in from the digestive gland or '' liver," a paired dark brown mass surrounding the stomach. The intestine leads from the stomach as a narrow tube which makes several convolutions in the visceral mass, and passing backw^ard, opens into the exhalant siphon just over the posterior adductor muscle. The chief organ of the circulatory system is the heart, situated saddle-like upon the intestine, dorsally near the hinge. It con- sists of one ventricle and two auricles, and is inclosed in a membranous chamber, the pericardium. (This is the only body coelome possessed by the pelecypod.) The blood is a colorless liquid and forms an important part of the mass of the body. It is pumped by the ventricle into two aortae, the an- terior and the posterior, which branch into arteries and open sinuses, thus penetrating all parts of the body with its load of MOLLUSCA — PELECYPODS 213 food and oxygen. From these sinuses the blood is gathered up by veins and returned to the auricles, the larger part passing through the gills on its return. The excretory organs are the nephridia, a pair of dark, U-shaped tubes, of which one arm is glandular and spongy, the kidney, and the other is non-glandular and thin-walled, the bladder. They are situated in the postero-dorsal region. The kidney communicates with the pericardium and the bladder opens into the mantle cavity. Waste material gathered from the body by the blood is extracted from the blood by the kidneys and passed out of the body into the mantle cavity by the exterior opening of the bladder. The nervous system consists of three pairs of large ganglia and their connectives : a ganglion on each side of the oesoph- agus, united by a nerve cord and connected by other nerve cords with the two pedal ganglia in the base of the foot, and the two visceral ganglia near the posterior adductor muscle. Sense organs. — All of the soft parts are sensitive to touch, but this sense is especially well developed on the edges of the mantle and of the siphons. There are no definite eyes, but there are pigmented areas in the siphonal region, w^hich are sensitive to light, but which can distinguish no color or form. The osphradium is a small organ at the point of attachment of the gills whose function is supposed, from its situation, to be to test the water as it flows into the gills. It has been suggested that it may possess the undifferentiated chemical sense of smell and taste combined. The otocysts are spherical cavities filled with liquid in which is suspended a solid particle, the otolith. These are balancing organs, serving to keep the clam upright. They are supposed likewise to have an auditory function since pelecypods are able to sense sounds transmitted through the water. The following are some of the principal muscles of the body (Figs. 88, 89) : I . Mantle muscle. This extends around the edge of the man- 214 AN INTRODUCTION TO THE STUDY OF FOSSILS tie lobe and unites it to the shell. The mark left on the shell by this attached mantle edge is called the pallial line. 2. Siphonal. This is a specialized part of the mantle muscle, originating from the siphons and serving to draw them into the shell. It spreads out fan-wise in proportion to the length of the siphons, and its insertion on the valve interrupts the evenly curved hne of attachment of the mantle muscle. Hence the pallial line is indented by the pallial sinus. 3. Adductor. These are two large cylindrical muscles which pass transversely across the body and are attached at each end to one of the valves ; their insertion leaves on each valve an anterior and a posterior muscle impression. The contraction of these muscles pulls the valves together and closes the shell : a chitinous ligament, tough and elastic, unites the valves ex- ternally. This, like a C-spring, exerts a constant tendency to straighten and thus to cause the valves to open to a certain ex- tent. Beyond that distance it tends to prevent the valves from opening. When the adductor muscles, therefore, relax, the valves yield to the action of the ligament and open. 4. Foot 7nuscles. The foot is drawn into the shell by the anterior and posterior retractor muscles and is extruded by a single protractor muscle which spreads fan-like over the whole visceral mass and by the compression of which the foot is forced out. The attachment of these muscles is marked by three faint scars on each valve — that of the anterior retractor and the protractor near the anterior adductor impression, and that of the posterior retractor just dorsal to the posterior adductor. The foot itself is likewise very muscular. That part of the mantle which is outside the pallial line is free, is somewhat thickened and contains shell-building glands. This series of glands around the edge of the mantle secretes a somewhat viscous liquid containing carbonate of lime, a shell material probably derived from the blood by the epithehal cells of the mantle margin. This hardens at once into a layer of shelly matter deposited around the edges of the shell aper- MOLLUSCA — PELECYPODS 215 ture. Thus the shell grows by the continual building out of its edge through successive depositions of lime and of conchiolin. In this way are formed the two outer of the three layers of which the shell consists. A transverse section through a valve reveals (i) an outer horn-like layer of conchioUn secreted only by the extreme edge of the mantle and hence always projecting slightly in advance of the other layers ; (2) a middle prismatic layer composed of calcareous prisms placed at right angles to the shell surface ; and (3) an inner pearly layer, composed of thin alternate layers of calcareous matter and of conchiolin, parallel to the shell surface. This presence of conchiolin throughout the shell furnishes it with a sort of membranous framework sufficient in amount to enable the shell to retain its shape after the re- moval by acids of all calcareous matter. After the glands around the edge of the mantle have secreted these layers in the manner described, other glands covering the whole external surface of the mantle line the shell thus formed with the inner pearly layer. When the seasons, temperature or food supply are unfavor- able to rapid growth, the mantle does not in- crease in size. The glands which secrete the shelly matter con- tinue active, however, and their deposit forms an extra thickness on the shell alreadv Fig. 91. — The quahog, Venus mercenaria Linne, showing how age may be reckoned by counting the more prominent growth lines. Three and a half years old ; three inches long. At the same time each year a notch was filed into the edge of the shell. (Redrawn from Belding.) formed, especially around its edge. With the return of con- ditions favorable to the growth of the animal the mantle 2l6 AN INTRODUCTION TO THE STUDY OF FOSSILS grows forward, again extending the shell and leaving behind as a thickened line the deposit of shelly material formed during the quiescent stage. The shell thus bears a succession of raised lines of growth or varices (Fig. 91), indicating inactive periods and separated by thinner bands marking periods of active expanding growth of the mantle. There may be many such growth lines in a year, as favorable and unfavorable condi- tions alternate, minor oscillations in conditions as that between high and low tide, day and night, etc., being indicated by very fine growth lines. The dorsal or cardinal margin of each valve is strengthened by a thick vertical plate, the hinge plate. Upon this are strong projections and ridges forming a system of teeth and sockets, the teeth of one valve fitting into the sockets of the other. This interlocking apparatus constitutes the hinge of the shell ; by means of this an exact closure of the valves necessarily oc- curs. The teeth are of two kinds, the anterior or cardinal, consisting of short transverse elevations, and the posterior or lateral, longer teeth parallel with the dorsal margin of the valve. The rounded, elevated portion of each valve is called the umbo; it ends in a point, the beak, which curves toward the anterior end of the shell. This is the oldest portion of the shell and from it grow^th has proceeded. Hence the beak is the initial point of the concentric growth lines. Under the beak and an- terior to it is a depression called the liinule. The sexes are distinct. The reproductive elements are ex- truded into the mantle chamber and out into the surrounding water through the exhalant siphon. Millions of eggs and spermatozoa are produced, most of which perish, since it is only by chance that their union is effected and fertilization thus results. Development starts directly in the fertilized egg ; this results in the formation of a blastula which soon invaginates, thus passing into the gastrula stage. Thus, about ten hours after the egg has been fertilized, the embryo has become a spherical MOLLUSCA — PELECYPODS 217 gastrula yf-Q of a millimeter in diameter. Up to this time it has remained inclosed in the gelatinous case which covered the egg, but in its gastrula form it is provided Vvith hair-like ciHa which start it rapidly revolving, and soon it breaks through the transparent egg case and escapes as a trochosphere larva into the water. This trochosphere stage is characterized by a top- shaped body with cilia confined to the blunt anterior end, by a primitive mouth and by the appearance of a shell gland opposite the mouth. During the next twenty-four hours a tiny valve, secreted by the shell gland, forms on each side of the animal and slowly increases in size until it completely envelops the embryo. The dorsal portion alone remains uncalcified and by additions of conchiolin it develops into the C-spring ligament. Other changes taking place along with the formation of this shell are the development of a velum, — a peculiar kind of extensible ciliated swimming organ, the development of a foot and the increasing complication of the digestive tract. This shelled swimming form, succeeding the shell-less swimming trocho- sphere, is called the veliger. All these changes, from gastrula to veliger, are accompanied by but small increase in size ; but at the end of the veliger period, which endures from six to twelve days, according to the temperature of the water, important changes are inaugurated which lead rapidly toward the attain- ment of the adult form. The animal increases in size, and with the complete disappearance of the velum and the loss of the swimming function of the foot, it leaves the free swimming life and sinks to the bottom. A gland in the foot secretes the hyssus, fine, tough threads by which the animal becomes attached to sand grains, shells, eel-grass or other objects. It is, however, an active animal at this stage and constantly travels from one place of attachment to another, breaking its byssal threads and forming new ones. The addition to the shell from this time on is coarser, whiter, and characterized by well-marked concentric growth lines. A 2l8 AN INTRODUCTION TO THE STUDY OF FOSSILS sharp line separates this new shell growth from the earlier larval shell, — the prodissoconch, which had a smooth, homogeneous structure (compare Fig. loo, pd.). During this attached stage the various organs of the body slowly take on adult characteristics. The clam remains at- tached until it has become large enough to make its way into the sand. When it is about 9 mm. long the byssus disappears and the active foot burrows into the sand, pulling the shell after it in a series of jerks, the siphonal end of the animal being left projecting upward in the burrow. Hereafter it moves but little, occasionally, however, crawling short distances. Though the young clams sustain heavy losses before they become able to burrow, the adult animal is one of the hardiest of pelecypods. It is very insensible to temperature changes and to changes in the saltness of the surrounding water, and it can endure long exposure to the air. There are few natural enemies of the adult clam. Even the starfish and oyster drill are not very destructive. They are known to live four or five years and perhaps in some cases longer. Growth is most active in August, being nearly at a standstill from November i to May i. One indi- vidual with length of an inch when measured was found to have grown | of an inch the following year. Fertilization (in New England) occurs from early June to the middle of August. 1 . What is the common name of Venus mercenaria ? 2. Its present range of habitat? Its geologic range? 3. Examine the specimens preserved in alcohol : {a) with valves held apart exhibiting relation of mantle to shell, the gills, muscles and foot ; {b) with one valve raised preserving attachment at hinge, showing upon the mantle the following muscles and upon the shell their attachment scars: (i) mantle, (2) siphonal, (3) adductor, and (4) foot. 4. Examine a dried specimen, sectioned through the two valves from ligament anteriorly, showing the ligament which opens the valves, one of the muscles which closes it, the lines marking the growth of each valve in length and thickness. (The MOLLUSCA — PELECYPODS 219 specimen should first be sectioned, then all the soft parts re- moved except the muscles, soaked in corrosive sublimate for a day or two, and thoroughly washed and dried.) 5. What is the mantle ? Its function ? What mark does it leave upon the shell ? 6. What are the siphons ? Their functions ? What mark does their presence make upon the shell and why ? 7. Compare a transverse section of this pelecypod to a book. 8. Explain in detail how respiration is effected. 9. What does the clam eat ? Explain the process of getting the food, its digestion and assimilation. 10. Describe briefly the blood circulatory system. 1 1 . How are the different waste products of the body thrown off? 12. Of what does the nervous system consist? 1 3 . Wha c sense organs does the clam possess ? Their function ? 14. Name four sets of muscles, explaining the function of each. 15. Describe in detail the growth of the shell. 16. What is the origin of pearls ? 17. Sketch the exterior of a valve, noting the umbo, beak, growth lines, lunule. 18. Why are the growth lines arranged concentrically? 19. Explain the occurrence of the few strong growth lines upon the shell. 20. How can the mantle secrete three lavers of shell ? 21. Sketch interior of a valve, locating hinge margin, liga- ment, hinge plate, teeth (cardinal and lateral), pallial line, pallial sinus, the two adductor and three foot muscles. 22. What is the function of the teeth ? 23. How is the foot protruded? 24. What is the relation of the pallial sinus to the siphons ? 25. How are the valves opened? How closed? Illustrate with sketches. 26. How do you distinguish the right from the left valve ? 27. Are the two sexes united in one individual? 28. Describe the development of the clam from the union of spermatozoon and ovum to its adult state. General Survey of Class Pelecypoda Pelecypods are compressed, usually symmetrical, mollusks protected by a calcareous shell of two, usually equal, valves 220 AN INTRODUCTION TO THE STUDY OF FOSSILS and possessing a ventral, often hatchet-shaped, foot capable of burrowing in sand. There is no distinct head, nearly the whole ventral aspect of the animal consisting of the muscular mass of the foot. The presence of a siphon in the various species of pelecypods is nearly always indicated on the valve by a pallial sinus (see page 214), though in a few exceptional species there is no such indication of its presence. When no pallial sinus is present, the pallial line is called simple. The portion of the mantle which is outside of the pallial line bears the pigment glands and in certain pelecypods papillae and tentacular processes. On this edge likewise are the visual organs when such are present, as in Pecten. Pearls are pathological products of the secreting function of the general mantle surface, not of its edge. Small foreign ob- jects, usually some parasites such as the larvae of certain worms, get between the mantle and the shell and set up an irritation there. The secretion of pearly deposit by the irritated glands around these offending objects results in pearls. (See also page 215.) All surface irregularities of the shell, such as lines, knobs, spines, etc., are simply the result of corresponding modifications of the margin of the mantle. Thus spines indicate the exist- ence of finger-like projections extending out from the edge of the mantle and secreting around themselves these hollow shelly processes. Ribs on the shell indicate wavy undulations of the mantle margin. The hinge teeth are probably derived from the crenulations or ribbing of the surface of the shell. The digestive canal is much coiled, consisting of mouth oesophagus, stomach (into which open two large digestive glands) and intestine, ending in an anus. The blood of pelecypods con- tains nucleated amoeboid corpuscles and in some forms, such as Area pexata, — the bloody clam, some species of Tellina, etc., there are also present non-amoeboid corpuscles containing haemoglobin ; in such cases the blood is red. In other forms MOLLUSCA — PELECYPODS 221 (some Veneridae, Cardiidae, etc.) the blood is bluish, owing to the presence of haemocyanin. In Venus, Ostrea, Pecten, etc., it is nearly colorless. The nervous system consists typically of four pairs of ganglia, cerebral, pleural, pedal and visceral, united by nerve connec- tives. The usual sense organs are otocysts and osphradia. Eyes are at times present on the mantle edge ; these range from simple pigmented cells to the complicated eye of Pecten. The sexes are usually separate. The order Anatinacea is hermaphroditic, as also the Cyrenidae and certain other isolated genera and certain species of Pecten, Ostrea, Anodonta, etc. The valves are held together by one or two strong adductor muscles, passing transversely from valve to valve, and their opening is effected, upon relaxation of this muscular tension, by external or internal ligaments. The external ligament, acting on the principle of a C-spring, is exemplified in Venus (Fig. S>g,A). The internal ligament (resilium) functions as would a piece of elastic rubber between a door and its jamb. Its triangular shape (narrower at the hinge than internally) keeps the hinge portion of the valves firm while causing the opposite side to open. It may be single, as in Mactra and Ostrea (Fig. 95, /), or multiple, lying in a series of pits, as in Inoceramus. In some forms, such as Mactra, a special spoon-shaped projection from the hinge, the resilifer, or ligament pit, lodges the internal ligament. The ligament, whether external, or internal, is, in its origin, continu- ous with the shell, being the part of the original embryonic shell which remained uncalcified. The dorsal hinge of interlocking teeth necessitates an exact closure of the valves so that even at the approach of danger, when the valves are hastily closed, they will meet edge to edge and thus prevent the access of any enemy to the soft and tempting body portion. The two valves are usually similar in size and appearance, one being the " mirror image " of the other. They are distin- guished as the right and the left valve, that to the right and 22 2 AN INTRODUCTION TO THE STUDY OF FOSSILS left respectively, as the shell is held with beaks uppermost and with the anterior extremity directed outward. The following are the criteria for distinguishing the anterior and posterior ends of a valve. 1. The umbos are nearly always directed forwards. 2. The pallial sinus is posterior. 3. The external ligament is never entirely anterior, and is, usually mostly posterior to the beaks. 4. When there is but one adductor impression it is the pos- terior. Both pelecypods and brachiopods have an external, bivalved, calcareous shell. That of the former diiTers from that of the latter as follows : — 1. Valves are right and left, not dorsal and ventral. 2. Valves are usually inequilateral and equivalved. 3. Umbos are never perforated by a pedicle opening. 4. Teeth when evident are present in both valves. 5. Ligament is present. Shell accessories are present in some genera, such are de- scribed under Teredo. The anterior adductor muscle may become diminished in importance or entirely absent. In such a case the posterior adductor necessarily assumes a more central position as a result of the greater demand placed on it for mechanical efficiency. The disappearance of the anterior adductor and the assumption by the posterior of a more central position are accompanied by a shortening of the antero-posterior axis of the shell and a proportional lengthening of the dorso-ventral axis. Such a transformation has been effected in the oyster (Fig. 95). Pelecypods range from the lower Paleozoic to the present time, being, however, extremely rare in the Cambrian, where they are represented by a very few doubtful genera, such as Fordilla. Fordilla is oval, concentrically striated, and some- what similar in appearance to Estheria of the Crustacea, with which it is at times classed. MOLLUSCA — PELECYPODS 223 ^p.a. 92. Derivation of name. — Greek pelekus, an ax, -\- pons (pod), foot. The foot of many pelecypods is shaped like an ancient battle ax. Nucula (Fig. 92). Ordovician to present. Valves small, oval or triangular, with a pearly interior. Hinge line taxodont, i.e. bearing a series of small, nearly equal, transverse teeth. Beak exceptional in facing the posterior end of the shell, i.e. the beak faces away ><#^^:^^|^ Cf.U. from the mouth, which is near the an- terior edge of the shell. Mantle lobes free, without siphons, /\ hence pallial line yig simple. Two adduc- tor muscles present. Name from Latin nucula, a little nut. Especially abun- dant in the Hamilton, Pennsylvanian and Cretaceous of North America, but widely represented by both fossil and recent forms in Europe and Asia as well. 1. How do the beaks of Nucula differ from those of most other pelecypods ? How is this known ? 2. Sketch an interior view of one valve, indicating anterior and posterior ends, beak, hinge Une, teeth, muscle scars, pallial line. 3. What is the function of the teeth ? 4. Mention three characters which determine this to be a pelecypod shell rather than a brachiopod. 5. What is the probable origin of teeth in pelecypods ? Inoceramus (Fig. 93). Jurassic to Cretaceous. Valves unequal. Hinge line long, straight, without teeth, but with numerous small, transverse ligament pits. Surface Nucula proxinia Say, from the Miocene of Maryland. Natural size. /I, exterior of left valve. B, interior of right valve showing the two muscle scars and the numerous teeth in a row (taxodont dentition), a.a., anterior adductor muscle scar; p.a., posterior adductor muscle scar. (From Glenn.) 224 AN INTRODUCTION TO THE STUDY OF FOSSILS marked by coarse concentric undulations. This genus is especially characteristic of the Cretaceous. Fig. 93. — Inoceramus barabini Morton, from Montana. This pelecypod abounded in the shallow waters of the large ocean which cut North America into an eastern and a western continent during Cretaceous times. A, hinge view of entire shell. The valves are separated posteriorly, and the beaks have been slightly displaced ; the absence of articulating teeth renders such displacement, through the weight of sediment, very easy. B, outer surface of left valve of same specimen. Natural size of a small individual. 1. Sketch {a) hinge view of combined valves ; {h) outer surface of one valve. Label in sketches umbo, hinge line, growth ridges, oldest portion of shell, youngest portion, right valve, left valve. 2. Distinguish between umbo and beak. 3. What was the function of the row of pits along the hinge line ? 4. Account for the slipping of one valve past the other in most specimens, so that the edges of the valves do not meet edge to edge. This slipping seldom occurs in such forms as Unio and Venus. Why ? 5. How are pelecypod shells thickened? 6. Is the shell external or internal ? Pteria. Ordovician to present. Shell oblique, inequilateral and inequivalved, with the left valve more convex than the right. Hinge line long, bearing one or two small cardinal teeth and a long lateral tooth. Pos- terior ear wing-like, longer than the anterior. Sinus for the passage of the byssus present under the right anterior ear. MOLLUSCA — PELECYPODS 225 Ligament in a groove, partly internal and partly external. Only posterior adductor scar present in adults. Meleagrina (Fig. 94), a sub-genus of Pteria, is of especial interest from the fact that one of its species, M. margaritifera, is the chief source of the white pearls of commerce. Pearl oysters are found especially in the East Indies. For the origin of pearls see page. 220. Fig. 95. — The common oyster, Ostrea virginica Gmelin, from the Atlantic coast of North .\merica. A , longitudinal section through the valves showing the opening ligament (/.), the closing or adductor muscle {a.m.), the an- terior progression of the muscle scar {m.s.), which in this species is black, and the internal thickening of the shell (/.) ; j., junction of the two valves; /'., ligament area; l.v., left valve; r.v., right valve. B, interior of right valve^ (Both X |.) Fig. 94. — The "pearl oyster," Melea- grina margaritifera, from tropical seas. (Xi) 1. Sketch exterior of one valve, noting wing, ear, byssal sinus. 2. How are pearls formed ? Ostrea (Fig. 95). Fennsylvanian to present. Shell irregular, at- tached when young to other objects by the left or larger valve. Beaks terminal. Left valve convex, right valve flat or concave. Structure of shell lamellar. Ex- ternal surface more or less distinctly ribbed. Teeth generally absent but hinge line broken by a triangular cavity for the ligament. Anterior 2 26 AN INTRODUCTION TO THE STUDY OF FOSSILS adductor impression absent, posterior nearly central. No siphons present. The shell becomes attached at the close of its free-swimming stage as soon as it settles to the bottom of the water. The mantle at the front (ventral) edge of the left valve when coming in contact with some foreign object secretes a cement similar to the organic material within the shell itself. Oyster shells are very often found to be completely riddled with small holes, the work of the boring sponge, Cliona sul- phur ea. Fossil oysters are found in North America, Europe, and India. They are especially abundant in the Cretaceous of America and in the Tertiary of the coast states. A brackish water form, living in tropical and temperate seas, the oyster thrives best in clear water close to the shore where the water is fresher than in the open sea. * 1. Sketch interior view of one valve, noting the characteristic V-shaped ligament area and the muscle marking. 2. Explain the action of the ligament in opening or closing the shell. 3. How does Ostrea differ from Nucula in {a) number of muscle impressions ; {h) teeth ? 4. Discuss the reason for the central location of the posterior adductor impression. 5. Is Ostrea attached or free during life? How can this be told from the shell ? 6. In what kind of water does it usually live ? 7. The oyster is a good example of adaptation to a sedentary life. How does this show in the shell ? 8. Notice the difference in the shape and size of the valves. Why is this desirable ? 9. Would such a heavy shell be satisfactory for the scallop (Pecten) ? Why ? 10. Sketch longitudinal vertical section of a valve, showing the progression of the muscle impression and thickening of the valve. 11. Why does CHona bore into such shells as the oyster ? MOLLUSCA PELECYPODS 227 Exogyra (Fig. 96). Upper Jurassic-Cretaceous. Attached like Ostrea by the left valve but distinguished by the strongly twisted beak of this valve. Right or upper valve usually fiat. Surface varying from nearly smooth to strongly A B Fig. g6. — The oyster-like pelecypod, Exogyra arietina Roemer, from the Del Rio clay of the Washita formation (uppermost Comanchean) of Texas. A, right valve shown in place within the larger left valve. (After Hill.) B, outer view of a slightly imperfect left valve. C, inner view of same; ad., adductor muscle scar; /., liga- ment groove. Natural size. plicate. The name refers to the twisted beaks from the Greek cxo, out, + gyros, a curve. ^ij^^r:'-i ^ J* k^^^ "•^^^^.l^jC. Fig. 97. — An oyster-like bed formed by Exogyra arietina in the ancient seas covering much of Texas during uppermost Comanchean (Del Rio) time. See Fig. 96. (X i) (From Hill.; 228 AN INTRODUCTION TO THE STUDY OF FOSSILS Very characteristic of the Comanchean of Texas and of the Cretaceous of both the western and eastern states. E. arietina, at times, as in the Del Rio clay of the Texas Washita, occurs in enormous quantities, forming solid beds up to six inches thick (Fig. 97)- 1. Name one similarity to Ostrea ; one difference between the two forms. 2. At what time in the life of the individual Exogyra does it become attached to a foreign object ? Reasons. 3. Sketch interior view of left valve, indicating muscle im- pression and ligament groove. 4. How is this known to be a pelecypod and not a gastropod ? Unio (Fig. 98). Jurassic to present. Valves of equal size, with a thick, brown, horny epidermis developed as a protection against the carbonic and humic acids in the fresh water as well as against the movement of the water itself. Shell thick, with a hinge line of heavy, indefinitely shaped teeth. External ligament present. There are no true siphons, simply openings between the mantle edges for incurrent and excurrent water. The animal grows slowly and may live fifteen or twenty years. The name is derived from the Latin unio, a pearl ; the shells are occasionally pearl-bearing. These are the " river mussels " found at the bottom of lakes, ponds, or running streams in all parts of the world, more espe- cially in the northern hemisphere. They rest erect with valves slightly gaping, partly buried in the mud and sand ; if disturbed, the foot and mantle edge are drawn into the shell and the valves shut tightly. The sexes are distinct. The eggs are fertilized within the body by spermatozoa introduced with the respiratory current ; these fertilized eggs are passed into the cavities of the outer gills, where they are nourished by a secretion from their walls. The larvae are thrown out through the exhalent siphon. The presence of these developing young cause the shell of the female to be more arched than that of the male. MOLLUSCA — PELECYPODS 229 There are more than one thousand living species. In the fossil state the genus is especially well represented in the Cre- taceous of the Rocky Mountains. cur. a.a. Greek cepkale, head, -{-pons {pod), foot. The foot of other mollusks is here transformed into the arms and funnel about the head. Cephalopods are divided on the basis of the number of gills, into two orders. 1. Tetrabranchiata. 2. Dibranchiata. Order i, Tetrabranchiata Cephalopods possessing an external shell of many chambers, only the last of which is occupied by the body of the animal. Head region bearing many appendages with suckers, and saucer- shaped eyes open to the exterior and without lenses. Four gills and four kidneys present, but no ink sac. Named in reference to the number of gills from Greek tetra, four, + branchia, gills. This order is represented by but one living genus, Nautilus, which has flourished from Tertiary to present times. There are, however, a great many fossil cephalopods found in Paleozoic and Mesozoic rocks which, though not affording much informa- MOLLUSCA — CEPHALOPODS 261 tion as regards the anatomy of the living animal, such as the number of gills and kidneys, are classed with this order because their shells agree closely with that of Nautilus. Cephalopods have been the strongest competitors of the ver- tebrates in the oceans from Silurian time to the present. Sections through the living chambers of different Paleozoic species show scales or other armor of the fish then living, indicat- ing that such animals formed part of their food. This order includes the two great groups Nautiloidea and Ammonoidea ; the former have a non-calcareous and the latter a large calcareous initial chamber, the protoconch (Fig. 116, pr.). The siphuncle in the nautiloids varies in position from dorsal to ventral, being often centrally placed ; in ammonoids it is, with the exception of one group, ventral in position, i.e. upon the outer edge of the coil. The curved growth lines of the hyponomic sinus almost invariably indicate the ventral side. In general the size of the siphuncle decreases from the nautiloids, through the ammonoids and belemnoids, to the sepioids, where it is a mere rudiment, distinguished with difficulty. This same relative decrease in the size of the siphuncle is seen in the devel- opment of an individual ammonoid from youth to maturity. Bactrites with its straight shell, simple sutures, ventral, but sub- marginal, siphuncle, peculiar collars and large calcareous proto- conch may be transitional between the two groups, the Nauti- loidea and the Ammonoidea. Sub-order a, Nautiloidea. — Shells straight, curved, or coiled. Sutures simple, i.e. straight or undulated, never acutely angular. Living chamber usually with aperture notched by a hyponomic sinus for the passage of the funnel. Siphuncle usually central or dorsal, i.e. on inner margin of whorl, rarely ventral. Shells smooth or with simple ridges or nodes, never complexly orna- mented. Nautiloids are first known from the Cambrian rocks ; they reach their maximum development in the Silurian and decline to the Triassic ; since that period their retrogression has been 262 AN INTRODUCTION TO THE STUDY OF FOSSILS slight. At present they are represented only by the genus Nau- tilus, which has given the name to the sub-order. Orthoceras (Fig. 114). Ordovician to Triassic. Shell usually straight in the form of a long, tapering cone (whence the name from Greek orthos, straight, + ceras, a horn). Surface smooth. Living chamber long. Sutures simple, straight or nearly so. Siphuncle usually central. 1. Sketch {a) side view; {h) top view. Label sutures, living chamber if present, siphuncle. 2. How do you account for the succes- sion of chambers and their equal spacing ? 3. What was the function of the si- phuncle ? 4. What part of the body secreted the shell ? 5. What chamber did the body occupy at the time of the animal's death ? Was the siphuncle tilled or empty during life ? A post. Fig. 114. — Thecephal- opod, Orthoceras so- ciale Hall, from the marine Maquoketa formation (Upper Ordovician) of Iowa. ( X 2-) il, an almost complete internal mold of the shell showing the suture lines and probably most of the living chamber, ant., an- terior end ; l.ch., liv- ing chamber; post., posterior end ; su., suture. B, an ideal cross section showing the siphuncle {si.). {A, after Clarke.) Ryticeras (Fig. 115). Devonian. Shell varying from slightly curved to loosely coiled. Siphuncle ventral, slightly expanded between the septa. Surface marked by coarse bands and at times by spinous processes. I. Sketch side view, showing curve of shell. Nautilus (Figs. 112, 113). Tertiary to present. Four living species of Nautilus are known ; these are from the Indian and Pacific Oceans. N. pompilius is described on page 251. MOLLUSCA — CEPHALOPODS 263 Sub-order b, Ammonoidea. — Shell usually closely coiled in a flat spiral. Sutures more or less complex, at times acutely angular. • Siphuncle small, and situated near the ventral (outer) margin. Surface often highly ornamented with ridges and nodes. In some ammonoids the aperture of the shell was closed, after the withdrawal of the animal, by a plate corresponding in function to the operculum of the gastropods, and probably secreted by such a muscular lobe as the hood of Nautilus. Ammonites are especially important as index fossils in the Mesozoic. They are known from the Silurian to the Cretaceous inclusive. As this sub-order is wholly extinct, we are de- pendent for knowledge of the animal and its habits wholly upon the informa- tion afforded by the shell and the character of the rock in which it is found. It w^as probably closely comparable with Nautilus. A few were swimming forms as is indicated by the presence of a hyponomic sinus on the shell, the mark of the swimming organ, — the hyponome ; but most ammonites were apparently able only to crawl. The apertures of these latter have in place of the hyponomic sinus a pointed prolongation of the ventral portion of the shell, the rostrum. Fig. 115. — -Internal mold of the shell Ryticeras trivilve Conrad, from the Onondaga (Middle Devonian) of New York. ( X f .) sii., sutures. (From Hall.) Bactrites (Fig. 116). Devonian. Shell straight, gradually tapering, round or compressed ellip- tical in section (whence the name, from Greek badron, a staff, 264 AN INTRODUCTION TO THE STUDY OF FOSSILS su:..: ^sl D Fig. 116. — Bactrites gra- cilior Clarke, from the Naples beds (Upper Devonian) of New York. A, a nearly en- tire shell (X f). 5, an ideal longitudinal sec- tion showing septum {sp.), suture {su.), and siphuncle {sL). C ( X 20), apex of shell show- ing protoconch (pr.) and, where the shell is broken away, the su- tures (su.). D, upper surface of a septum showing siphuncle (sL). (After Clarke.) + ites, meaning stone). Sutures simple except for the small ventral lobe. Si- phuncle ventral, sub-marginal. 1. Sketch (a) side view showing ventral lobe ; (b) top view ; label sutures, ventral lobe, siphuncle. 2. Why is this not included with the sub- order Nautiloidea ? Muensteroceras (Fig. 117). Mississippian. Shell coiled into a thick disk. UmbiHcus moderately wide, with angular margin. Sutures with angular lateral lobe and broad lateral saddle, and with a narrow lobe on the venter broken by a small notched saddle. All shells with the above type of simply angular sutures were formerly classed as goniatites (from Greek gona, a knee). 1. Sketch view showing coils, noting su- tures, lobes, saddles, umbilicus ; indicate the ventral side. 2. How was the umbilicus formed ? 3. Sketch an entire suture from venter to umbilicus. 4. What is a suture ? 5. What determines the dorsal and ven- tral sides of a shell ? Placenticeras (Fig. 118). Cretaceous. Shell coiled into a thin disk. Suture complex, made up of numerous serrated lobes and saddles (the ammonitic type of suture) ; the third lateral lobe is the deepest, after which there is an abrupt decrease. MOLLUSCA — CEPHALOPODS 265 1. Sketch (a) circular view of specimen showing sutures; (b) view showing aperture. 2. What is the relation between septum and suture ? 3. Under what conditions do sutures become visible? Umb\'K A 8 Fig. 117. — An ammonite, Muensteroceras oweni Hall, abounding in the ocean cover- ing Indiana during Kinderhook (Lower Mississippian) time. Natural size. A , side view. B, ventral view. Sutures goniatitic ; /./., lateral lobe ; l.s., lateral saddle ; umb., umbilicus ; v.l., ventral lobe ; v.s., ventral saddle. (Redrawn from Hall.) Scaphites (Fig. 119). Cretaceous. Coiled in a plane spiral with the whorls in contact and embrac- ing, except the last, which often becomes somewhat uncoiled and detached from the spiral and recurved in the form of a hook. Surface ornamented with bifurcating ribs which often bear tubercles ; ribs continuous across the venter. Sutures generally much divided with several auxiliary lobes. Name from Greek scaphe, a boat, + ites, meaning stone, in reference to the shape. The variety S. nodosus brevis is exceedingly abundant in the Cretaceous of the Rocky Mountain region, also in New Jersey. 1 . Sketch (a) view of spiral ; (b) apertural view ; (c) interior of section of entire shell cut parallel to the plane of coiling ; note siphuncle, sutures, ribs, septa. 2. How mlich of the entire shell did the body of the animal occupy during Ufe ? Compare with gastropods. 266 AN INTRODUCTION TO THE STUDY OF FOSSILS 3. On shell i, (c) follow a septum from its center to its outer edges, — the sutures ; note it gradually changing from the simple, fiat septum into the very complex lobes and saddles of the Fig. 118. — The ammonite, Placenticeras intercaiare Meek, from the Pierre forma- tion (Cretaceous) of South Dakota. A, side view of specimen (x 5). B, aper- tural view. C, suture of same from siphuncle (upon the outer edge of the coil) to umbilicus (umb.). si., siphuncle. (From Meek.) sutures. ( A section of any ammonoid shell will show the same change.) Compare this with a similar section through a fossil Nautilus ; what difference do you note ? 4. What principally distinguishes the Ammonoidea from the Nautiloidea ? MOLLUSCA — CEPHALOPODS 267 5. Distinguish the ammonitic type of suture from the goni- atitic ; give examples of each. c^;i Fig. 119. — Scaphites nodosus, var. brems Meek. An entire shell from the Pierre (Cretaceous) of Montana. A, view of opening of living chamber ( X f). B, side view. C, the suture ( X i^) extending from the position of the siphuncle ("upon the outer edge of the coil) to the unbilicus {umb.). si., siphuncle. (From Meek.) Baculites (Fig. 120). Cretaceous. Straight (except the first-formed part, w*hich is spiral), ellip- tical in section. Sutures with the lobes symmetrically divided. Named from its shape, from Latin baculum, a staff, + ites, meaning stone. B. compressus is abundant, associated both east and west with the variety of Scaphites noted above and with several species of the pelecypod Inoceramus. 268 AN INTRODUCTION TO THE STUDY OF FOSSILS 1. Sketch (a) the elongate flattened surface of a specimen showing the sutures ; (b) top view ; label sutures, lobes, saddles, umbilicus, septum, siphuncle. 2. These fossils usually occur with mud filling all the chambers. How did the mud penetrate the chambers ? 3. Distinguish between septa and sutures. 4. What does a single perfect shell of Baculites suggest as to its ancestry ? xao X40 XS Fig. 120. — Baculiles compress us Say, from the Cretaceous of South Dakota, i. A young shell preserving the early coils. The living chamber occupied about one half the length of the shell. 2. A specimen of same size as the last but with the outer shell broken away revealing the sutures, — the outer edges of the septa. Note the variation in the sutures from the apex of shell 2 to its wide end and on through the progressively larger shells as shown in 3, 4, 5, and 6. 6 represents the condition of the suture in the adult shell. (After Brown.) Order 2, Dibranchiata Cephalopods with shell internal or wanting, or exceptionally external but not chambered (Argonauta). Head bearing eight or ten arms around the mouth ; these are furnished with suckers. The eyes are very large and of complex structure. Two gills and two kidneys are present. An ink sac discharges its contents through the funnel when the animal is startled, thus constituting MOLLUSCA — CEPHALOPODS 269 a means of defense, since under cover of the blackened water the animal may escape. Indications of this ink bag are often present in fossil forms in the shape of an external mold of the sac, and even in carbon particles, the remains of the ink itself. The typical internal shell is seen in Belemnites, a fossil form described below. The shell is absent in the devil-fish (Octopus). The Dibranchiata are known from the Triassic to the present. r'"'^-, f-J^ff' r..i^ j-W'"'""" ^''1 '■l"'JI»'> Fig. 121. — An American squid, Ommastrephes illecebrosa Les. ( X i), from the Atlantic Ocean at Provincetown, Mass. A, dorsal view. B, side view of animal asleep ; note how the water for respiration is kept pure by the elevation of the anterior mantle slit above the mud. C, the jaws in position. D, side view of tip of skeleton. E, upper view of entire skeleton. (All drawn from life by J. Henry Blake.) Ommastrephes (Fig. 121). Living. This marine, free-swimming animal is world-wide in its distribution. In general all forms similar to this genus are commonly called squids. It has a distinct head bearing ten long, very muscular arms and two large, highly developed eyes ; two of the arms are much larger than the other eight. The head is separated from the trunk by a constricted region, the neck. The trunk is elongate, shield-shaped, bordered laterally by a fleshy fin. The entire body is surrounded by a thick muscular mantle which is free from the body except along the median dorsal line. 270 AN INTRODUCTION TO THE STUDY OF FOSSILS The skeleton is entirely internal ; it consists principally of the narrow pen of conchiolin (Fig. 121 D,E) passing the entire length of the trunk and protecting the visceral organs dorsally. There are, in addition, several somewhat horny cartilages which are supporting and protective in function. The cranial cartilage pro- tects the principal nerve centers and supports the eyes ; other cartilages support the bases of the fins and the arm bases. Another protective organ is the ink sac. This is located in the posterior part of the trunk and secretes a dark brown substance. When the squid is startled, it discharges this fluid through the duct opening within the anus, where, mixing with the water in the mantle cavity, it is discharged through the funnel as a black cloud under cover of which the animal escapes. Locomotion. — The squid can dart with great rapidity, partly by the arms, partly by the muscular, lateral fins, but principally by the rhythmical contraction of the mantle. The expansion of the mantle draws water through the slit between the anterior edge of the mantle and the body into the mantle cavity. Muscles then close this opening and the contraction of the mantle forces the water out through the funnel, causing the ani- mal to move in the opposite direction. It can move in any direc- tion by simply bending the funnel in the direction opposite to that in which it wishes to move. A valve prevents the water from entering the mantle cavity through the funnel. The SimmsLVsfood consists of mollusks, crustaceans, and fishes which it catches with its arms. The arms are furnished on the inside with many suckers. Each sucker is a shallow cup supported on a short stalk ; its membranous lip is lined internally by a narrow, horny rim and in the middle of the bottom of the cup is a piston-Uke plug which, when drawn down by the contraction of muscles, pro- duces, when held against a solid object, a partial vacuum and resulting adhesion. The prey stands little chance of escape when surrounded by arms lined by hundreds of such suckers. The eyes are much more perfect than those of Nautilus, and are next in order of development to those of the vertebrate. MOLLUSCA — CEPHALOPODS 271 Light rays passing through the protec- tive transparent cornea are bent towards the pupil by the water iilUng the external chamber of the eye ; this chamber is open by a small hole to the sea water. The pupil is an opening through the firm wall of the eye ; the portion of this wall im- mediately bounding the pupil and called the iris contains muscle libers by whose action the pupil can, to a limited extent, be enlarged or diminished. The light is then focused upon the retina by passing through the spherical, dense lens and next through the large mass of jelly-like vitreous humor. There are two otocysts in the posterior portion of the head ; these have the power of coordinating movements in maintain- ing equilibrium, and are possibly also functional in hearing. There may also be present a sense of smell and of taste. The sexes are distinct. The eggs are fertilized through copulation. Belemnites (Fig. 122). Jurassic to Cretaceous. Belemnites is closely related to the squid. Impressions of the tentacles and arms are sometimes found preserved in the fossil state, showing the suckers pro- vided with horny hooks. The mandibles and ink sac are likewise at times found >with the ink preserved in the form of solid carbon particles. The shell, however, is more complete than that of the squid, consisting of three parts, — guard, phrag- mocone, and proostracum. The guard is ai Ew m^5M ■^ ,H|N -^ ^ S 2 CQ QJ / 272 AN INTRODUCTION TO THE STUDY OF FOSSILS solid, and when examined in section is seen to be composed of prisms of calcite radiating from an axial line slightly nearer the ventral surface. The phragmocone fits into the hollowed end of the guard — the alveolus, and is divided into chambers by septa which are perforated by the ventrally placed si- phuncle ; this is followed by the calcified, blade-like proostra- cum. The proostracum corresponds to the pen of the squid and probably in life afforded dorsal protection to the viscera. The phragmocone corresponds to the entire shell of the Tetra- branchiata. •As an index fossil of the Jurassic and Cretaceous it is scarcely less important than the ammonites. The name, from the Greek belemnos, a dart, was given by Agricola in 1546. It is commonly called *' arrowhead " or '' finger stone " from the shape, and '' thunderbolt " or " thunder stone " from its supposed origin. 1. Split the broad end of a specimen longitudinally from the ventral groove backwards (if the narrower end splits likewise, this should be glued into place again). Sketch view showing this section. Label alveolus, guard. 2. Note the calcareous, prismatic fibers of which the guard is composed, and the successive conical layers by means of which the guard increases in ^ize. Make a cross section showing this increase. 3. The walls of the alveolus usually show faint impressions of the chambered phragmocone, the siphuncle of which was located ventraUy, i.e. upon the side next the ventral groove. Indicate upon the first sketch the ventral and dorsal sides. 4. What is the significance of the name Belemnites ? In the genus Sepia (Tertiary to present) the shell is likewise internal but extends the entire length and breadth of the body. It is without differentiated phragmocone and guard, but consists essentially of proostracum or " pen." The projecting point may represent the guard. This is the familiar cuttle bone of commerce. Sepia officinalis is very common in the Mediter- ranean. The coloring matter from its ink sac is insoluble in MOLLUSCA — CEPHALOPODS 273 water and gives a beautiful brown color much used in mono- chrome drawing. Other living genera of the Dibranchiata are the devil-fish (Octopus) and the Argonaut. Common American squids are Loligo and Ommastrephes. PHYLUM XI, ARTHROPODA The Arthropoda are transversely segmented animals with mouth and anus at opposite ends of an elongate body, with muscles attached to the inside of an external skeleton (the very opposite of the vertebrates), and with a nervous system composed of a dorsal brain above the oesophagus, connected by nerves around this with a double ventral chain of segmentally arranged ganglia. A few or most of the body segments bear paired append- ages, the distinct segments of which latter are separated by joints and moved by special muscles. Thus, as the animal does not need the movement of the skin for locomotion (as in the annulate worms) the skin secretes a horn-like substance, chitin, to form a hard outside skeleton. Since this rigid exoskeleton prevents increase in size, growth can occur only through the shedding or molting of this chitin. Eyes are nearly always present and are simple or compound. The cavity of the body between the exoskeleton and the internal organs consists largely of spaces, the blood sinuses, which are in full communication with the blood circulatory system. The heart, usually present, is elongate and is situated in a blood sinus from which the blood enters by valvular openings (ostia) . Arthropods are probably descended from some annelid worm- like ancestor, the crustaceans continuing to live in the water, while the insects, myriopods and most of the arachnids are di- verging to a life upon the land. Derivation of name. — Greek arthron, ]o\\\t, + pous (pod), foot, referring to the division of the limbs into movable segments. The phylum is subdivided as follows : — Sub-phylum i, Branchiata. — Mostly water breathers; breathe by gills (branchiae). 274 ARTHROPOD A — CRUSTACEA 275 Page Class A. Crustacea 275 Sub-phylum 2, Tracheata (except many of Class D). — Air breathers ; breathe mostly by tracheae. Class B. Onychophora 308 Class C. Myriopoda 309 Class D. Arachnida 309 Class E. Insecta ,.... 317 CLASS A, CRUSTACEA Type of the class, Camhariis (Fig. 123). The crayfish, Cambarus, lives in fresh water lakes, rivers and pools and is found in North America east of the Rockies and in eastern Asia. The only other genus of crayfish living in the northern Hemisphere is Astacus ; it is found in North America west of the Rockies, in Europe and in western Asia. There are also some blind crayfish of the genus Cambarus inhab- iting the caves in Carniola, southern Austria, w^hich point to the former more extended occupation of Europe likewise by this genus. The body is divided externally into the anterior unjointed portion, — the cephalothorax (union of head and thorax) covered with the carapace, and the posterior portion, the abdo- men, made up of distinct segments and terminating in the large horizontally flattened telson. The cephalothorax bears the eyes, feelers, and the five large walking legs. This division into head, thorax and abdomen is not equivalent to the like division of the vertebrate body. The body consists of twenty segments bearing upon their under side nineteen pairs of appendages. As can be seen by the ap- pendages on the ventral side, the head consists of five segments bearing pairs of antennae or feelers, the short and the long, one of mandibles or jaws, and t\Vo of maxillae. The thorax is made up of eight segments bearing five large posterior or walking legs and three smaller anterior pairs or foot-jaws, with their 276 AN INTRODUCTION TO THE STUDY OF FOSSILS bases toothed for passing the food obtained by them forward to the mouth. The abdomen consists of seven segments, each of which except the last, or telson, bears a pair of appendages. In the female the five anterior pairs are small swimming feet or pleo- pods, while the sixth pair is much enlarged, each consisting of two flat- tened parts which with the telson compose the five-parted tail-fin, the principal organ of loco- motion. The male dif- fers only in having the anterior two pairs of pleopods converted into incomplete tubes for transferring the sperma- tozoa to the body of the female. The typical appendage consists of one or more basal joints, the proto- podite, which divides into two branches : an inner and ventral, the endopodite, and the outer and dorsal, theexopodite ; this latter division is largely respiratory in function. The skeleton is exter- nal and is both protec- tive and supporting to the muscles and other soft parts within. It is composed of chitin se- creted by the epidermis, and hardened with more Fig. 123. — The craj'fish, Camharus hartoni Fabr. ( X f ), from Colchester, Vermont. Dor- sal view; abd., abdomen; ant. i, anterior an- tennae ; ant. 2, posterior antennae ; ceph., cephal- othorax ; e., eye; J.j., foot jaws; g.c, gill- cover; pin., movable arm of pincer; tel., telson ; iv.l., walking legs (five pairs) ; XIV, fourteenth body segment or first abdominal segment ; XIX, nineteenth body segment. ARTHROPOD A — CRUSTACEA 277 or less lime carbonate. It is segmented because it is thickened with lime carbonate in those regions not subject to bending, but remains thin and hinge-like in the intermediate spaces. The carapace arises as a fold of the skin from the posterior margin of the head region ; dorsally it coalesces with the body segments, but at the sides it is free, forming the gill-covers (Fig. 123, g.c). As these covers are unattached below they permit the free entrance of water to the gills within, which lie between the sides of the carapace and the walls of the thorax proper. Fig. 124. — A young horseshoe crab, Limulus polyphemus, from the Massachusetts coast, mulling, abd., abdomen; ceph., cephalothorax ; e., a compound eye; e'., a simple eye ; I., legs ; «., newly molted portion ; 0., the edges of the old shell ; /., telson. Since the soft parts of the body are completely incased in resistant chitin, growth can take place only by a process of molting, — of shedding the chitinous covering periodically (see Fig. 124). This is thrown off as a distinct whole. Not. only is every part of the exterior shed, but also the lining of the oesophagus, stomach, and all of the intestine except the middle portion, though some internally shed chitin, however, as that of the stomach, does not leave the stomach, but is redigested. This molt, an exact copy of the exterior of the living animal, is shed about once a year during adult life, but oftener during the rapid growth of youth. 278 AN INTRODUCTION TO THE STUDY OF FOSSILS The process of molting has been described as follows, a de- scription holding true in general for all Crustacea : " Previous to the throwing off of the old skin a new soft one is formed in- side" (the epidermis secretes new layers of chitin), '' the lime is absorbed from the old shell in a dorsal line along the carapace, reaching from the rostrum to its posterior margin. Absorption also takes place at the joints of the limbs. The carapace now splits along this dorsal median line of absorption, the blood leaves the limbs, which are thus made flabbier, and by invol- untary muscular movements they are drawn, large claw and all, through the joints of the old shell. The anterior portion of the body is first drawn out through the dorsal vent, and lastly the tail. By means of the return of the blood to the limbs and the rapid absorption of water, the body . . . soon swells to a size far beyond that of the old shell " (2). The lime taken up by the blood by absorption previous to molting is used in hardening the new shell, doubtless aided by the lime carbonate from pieces of shells, sea urchin spines, discarded lining of the stomach, etc., which have been found in the stomachs of crayfish and other Crustacea. Beneath the epidermis is a layer of connective tissue, — the dermis to which the muscles are attached. They are thus fas- tened to and supported by the external skeleton. The muscular system consists principally of two longitudinal pairs of muscles, a large and complex ventral pair and a smaller simple dorsal pair, both extending the entire length of the abdomen and into the thorax from whose walls they arise. The dorsal pair or extensor muscles straighten the abdomen, while a portion (the flexor muscles) of the ventral pair bends it downward ; the quick contraction of these latter powerful muscles causes the crayfish to dart rapidly backwards. It moves forward by the action of the abdominal swimming feet. Of the five pairs of long thoracic legs the four posterior ones are used in walking, the large anterior one with its huge terminal pincer for defense and ofTense. Each tube-like section of one of ARTHROPODA — CRUSTACEA 279 CO (_ >» C O cij C *-> d, o o ^ en c3 (-1 c/i 4; — £ •-; V O "S £ ^ -Q "^ := o .-::: -a "^ rt -a c .,.ii •" O i> 11 '-' C ^ *-) -7) r- c See: ^ '^ 3 1^ o 4j C3 — - ^ •- , Q a ^ O (U c o c -- a> is V Q <^ a c3 8 w rt S o e en "O '-n OJ C O tc 8 tn S D .- G ' ■" , " ^*' en C 3 O ^1 •■-3 .— -1-1 .^ > c3 V tn c -ji: a-* o c3 c/] -, J-* o .£f I- _ ^ •r" -d x; ^ o c > O P a tn SCO C3 ?; r O 5 -o -=> S ►^ -C i-T - tn __ tn P (J C3 I o ' c 10 .2 >-< ci • "o O ui tn ^ -^ f u- P ^ i>: «2 C> r- O p " " o -^ OJ c 'c ■c 9 . C tn "■** ^^ - ^ .- != .S « g tn -g^ tn c 2 S -2 u C tn *^ rt -73 .2 c 2 ^• o D. V w o ■^ o 22 iJ *j C 3 tn rt r p "P r i^ *-> 4) s .~ o *-• ^ c '•" o ^ « 3 ii ^ ^^ . S £ '^'-^ N r • -p ^ •35 ^ i 5 o d « o !u 1) rt u rt f= "^ - o J~ S= «> »^ s— • u -0 I-I ^ Cj •^~) _o ■4— > r^ 'E i> s £ b£ ^ t* *. J2 >^ ■s Ui tn ,fl rt -1-) > *. p s ^ (r, -J-) bl 3 M-l -1-1 1- tn ^" J3 to 28o AN INTRODUCTION TO THE STUDY OF FOSSILS these is united to its fellow by a hinge-joint, hence movement can occur in but one plane, as at the knee and elbow in man; but since the axis of the hinge is different at successive joints, each entire leg can move in all directions. Movement is effected by an extensor and a flexor muscle fastened to the sides of each tube-like section and inserted in the sides of the proximal end of the next outer section; the movable arm of the pincer is similarly worked. Digestive system. — The food of the crayfish is varied ; it may be animal or plant, living or dead ; it is largely decaying animal matter. On account of their need of lime they are fond of stone- wort (Chara). The smaller particles of food caught by the toothed bases (gnathobases) of the three anterior pairs of tho- racic feet are carried forward by them to the mouth, as are the larger pieces caught by the huge claws. There the food is torn into bits by the toothed edges of the strongly calcified mandibles situated at its sides. Anteriorly the mouth is bounded by a single plate, — the upper lip (labrum or hypo- stome) ; posteriorly by a pair of delicate lobes, — the lower lip. The food passes from the mouth through the oesophagus to the gastric mill, a division of the stomach ; this is lined with chitin and has projecting into it from its walls three calcified teeth (see Fig. 125). The mill is so moved by two pairs of muscles extending from it to the thoracic skeleton that the three teeth meet in the middle and thus complete the comminution of food begun by the mandibles. The food then passes to the smaller or pyloric division of the stomach ; the numerous hairs which extend across this division act as a sieve to prevent all but the very fine food from passing on into the intestine. The stomach is thus merely a masticating and straining apparatus ; digestion takes place in the small intestine. Into this is poured from the single pair of digestive glands a yellow fluid which digests both the proteids and fats, combining thus the function of both pancreas and liver of the vertebrates. The undigested remnant passes out through the large intestine and finally through the ARTHROPODA — CRUSTACEA 281 anus, which is situated on the ventral surface of the telson. With the exception of the sharp downward bending to the mouth the digestive canal is a straight tube extending the length of the body. Since the oesophagus and stomach as well as the large intestine are formed by the inbending of the surface of the gastrula, they are formed from the ectoderm as is the surface layer (epider- mis) of the mature animals ; hence they similarly secrete a Hning of chitin which must be shed with each molt. Only the small intestine and its digestive glands are formed from the inner cell layer, the endoderm, of the gastrula stage. The absorption of the digested food takes place through the walls of the small intestine and its digestive glands directly into the blood (since the intestine is surrounded by a blood sinus) and thus finally into the heart. The blood circulatory system consists of a muscular heart in the dorsal part of the thorax, arteries, capillaries, blood sinuses (cavities without definite walls among the muscles and viscera) and veins. The rhythmical contraction of the heart forces the blood into seven arteries, which, dividing, extend into all parts of the body and finally into microscopic capillaries which terminate by open mouths in the blood sinuses. All blood sinuses communicate with the ventral sinus which runs the entire length of the abdomen and thorax, and conducts the blood to the veins on the gills. From the gills, veins carry it to the sac-like cavity (pericardial sinus) in which the heart is located. The blood enters the heart, upon the latter's rhythmical expansion, through three pairs of apertures wdth inwardly opening valves. The blood is a colorless fluid and all the corpuscles are similarly colorless {i.e. leucocytes.) When combined with oxygen it is bluish gray owing to the haemocyanin in the fluid (not in the corpuscles), which like haemoglobin in mammals has great affinity for oxygen ; it thus acts as the oxygen carrier from the gills to the tissues. Respiration is performed by the gills, aided probably by the inner surface of the gill covers which bound them externally. 282 AN INTRODUCTION TO THE STUDY OF FOSSILS Internally they are bounded by the wall of the thorax, since they are outpushings of the body wall. They are freely open below for the entrance of water. The renewal of fresh water is brought about by the vibratory movements of the exopodite of the max- illa, causing a current to set in over the gills from below and out in front. The gills thus excrete carbon dioxid. Another excretory organ is situated at the base of each posterior antenna ; this is the green gland which collects the uric acid, urea, etc., in a urinary sac and discharges it through a duct opening on the proximal segment of the antenna. The nervous system consists primarily of a brain in the dorsal region of the head united by nerve cords around the oesophagus to the anterior end of a ventral nerve cord. The former supplies the eye, antennae, etc. The latter is composed primarily of a double, ladder-like chain of ganglia united by connectives and extending to the posterior end of the body. Most segments have their own ganglia. The sense organs include those of touch, sight and possibly also smell and hearing. The setae on the two pairs of antennae are tactile as are those in many other parts of the body. These are hollow outgrowths of the epidermis and its chitinous covering and contain the end of a nerve fiber prolonged outward from the dermis. There are two compound eyes at the front of the head, and since the latter is firmly fixed to the thorax the eyes are raised on movable stalks. Each eye is covered with the protecting, transparent cornea, the surface chitin ; this is divided into very many four-sided facets. Beneath each facet is the eye proper, or ommatideum, optically separated from its neighbor by a black pigment. The outer portion of each ommatideum is the refractive vitreous body, which bends the light rays falling upon it downwards to the inner portion, the small retina. The retina is composed of very sensitive cells, the ends of the optic nerve fibers, and through these is connected with the brain. The pigment sur- rounding the ommatideum absorbs all light not reaching the nerve fibers, thus preventing a distortion of the imag 3. Each sep- ARTHROPODA — CRUSTACEA 283 arate division of the compound eye gives a complete image, but the resultant vision of the entire eye is not a mosaic, although each facet gives a different perspective from its neighbor. The re- sultant is a single image just as in man, where the two eyes, each with a different perspective, produce a single image. Some delicate setae upon the shorter, or anterior, pair of antennae are supposed to function as organs of smell. In the proximal segment of the shorter pair of antennae occurs a sac-like inbending of the surface chitin. This sac, the otocyst or statocyst, is in free communication with the water outside through a small opening guarded by hairs. It is lined with sensory feathered setae, similar in structure to the tactile setae, and contains some minute sand grains. One function of this organ has been shown to be the maintenance of equilibrium, similar to that of the semicircular canals in man. Gravity acting upon these grains brings them into contact with different setae as the body becomes tilted at different angles and through these setae corresponding sensations are produced in the neigh- boring nerves which transfer them to the brain. Probably these setae also take cognizance of the sound waves passing through the water and thus act likewise as organs of hearing. When the animal molts, the chitinous lining of this sac is also shed so that new^ sand grains must be gathered after each molt. Reproduction is sexual. The eggs are of considerable size with a large amount of yolk. They are fertilized immediately after extrusion and are fastened to the swimming legs of the female by a sticky secretion from glands on those appendages. The one-celled egg after fertilization rapidly develops into the blastula-like stage and this into the gastrula. Thickenings then develop in definite parts, forming the rudiments of the three anterior appendages of the head; this is the nauplius stage. After this the embryo rapidly passes into the form in which it is hatched, that is, it becomes adult in form but not in size. 1. What is the present habitat of Cambarus? 2. Name the principal external divisions of the body. 3. What are the divisions of a typical appendage ? 4. Is the skeleton internal, i.e. covered upon the outside by a renewing fleshy layer, or external ? 284 AN INTRODUCTION TO THE STUDY OF FOSSILS 5. What is the composition of the skeleton? What differ- ence in composition between the regions subject to bending and those not so subject ? 6. Why is molting necessary to growth ? 7. What parts of the body are thus renewed ? 8. How often does molting occur ? Describe the process. 9. Are the gills external to the body or internal ? How are they protected ? 10. Where are the muscles fastened ? How does this differ from the muscles of the Vertebrata ? 11. What are the principal muscles of the body? Give loca- tion and use. 12. How does the animal move? 13. Give three methods of progression used by the crayfish. 14. How do the muscles effect the complicated leg movement ? 15. What does Cambarus eat ? How is food procured ? 16. Describe digestion ; absorption. 17. Briefly trace the course of the blood through the body. What are its functions ? 18. How does the crayfish breathe? 19. Give three means by which the waste of the body is elimi- nated. 20. Of what does the nervous system consist ? 21. In effectiveness of response to environment, how does this system compare with that of the pelecypod ? The coral ? 22. What sense organs does Cambarus possess? Describe each. 23. Describe reproduction. General Survey of Class Crustacea Usually aquatic and carnivorous arthropods, with body divis- ible into head, thorax and abdomen. The body is inclosed by a protective and supporting chitinous cuticle which becomes much thickened with lime carbonate where no movement is required. The food, consisting largely of decaying animal matter, passes through the mouth usually into a large stomach, thence through a straight intestine to the exterior at the posterior end of the body. The anterior and posterior portions of the digestive canal are lined with chitin, which is continuous with ARTHOPOD A — CRUSTACEA — TRILOBITES 285 that of the exoskeleton ; only the middle portion is unlined and this alone develops outgrowths for secretion of digestive fluids and for absorption. A contractile heart forces the blood through the arteries to the surface of the body, whence it returns through the veins or open sinuses to the heart, passing on the way through the gills, where these are present. Respiration is by the general surface of the body or by gills (hollow offshoots of the thoracic walls or of the thoracic or abdominal limbs). The young usually passes through a series of larval stages, — the nauplius, zooea and mysis stages. Through successive molts the young animal increases in length by the addition of new segments anterior to the telsonic region. Abundant as fossils. Derivation of name. — Latin crusta, a crust, referring to the hard, crust-like, calcareo-chitinous skeleton completely inclos- ing the animal. The class Crustacea is divided into the following sub-classes : Page 1. Trilobita 285 2. Phyllopoda 299 3. Ostracoda 303 4. Copepoda 304 5. Cirripedia 305 6. Malacostraca 3o5 7. Stomatopoda 308 Sub-class i, Trilobita Type of the sub-class, Triarthrus (Fig. 126). Triarthrusis much more closely allied to Apus (see p. 299) than to the crayfish, or any other living form, but lacks the peculiar carapace and probably the long, anal processes of the former. These processes, however, are known to be present, extending backward from the ventral surface of the abdomen, in Neolenus serratus of the Burgess shale (mid-Cambrian) of British Colum- bia. The carapace is lacking in many species of the order Phyl- lopoda, to which Apus belongs ; this is true of the fresh water shrimp, Branchipus, and of the brine shrimp, Artemia, but in 286 AN INTRODUCTION TO THE STUDY OF FOSSILS ant. }■ cephaloTi thorax 1 py^idi, urn B thora%-_;^^ ceph. vm. diqt U:" \ "■■,■:/" Q n\Q. "'• Fig. 126. — The trilobite, Triarthrus becki Green, from the Utica shales (mid-Ordo- vician of eastern North America). This species flourished in the muddy portions of the ocean which then covered this region. A, dorsal view. B, ventral view. C, a transverse vertical section at second thoracic segment {A-C X i^). D, sl median longitudinal vertical section. E and F ( X 45), two molts of the larval (protaspis) stage ; the later molted one {F) has added to the pygidium an addi- tional segment ; in neither are any thoracic segments yet developed ; the head has five segments with the eye-lines extending from the first segment, a., anus; ant., antennules or feelers ; ax., axial lobe ; ceph., cephalon or head segment ; db., doublure; dig.t., digestive tube; e., eye lobe protecting the compound eye; en., endopodite; ex., exopodite; Ja.s., facial suture; fi.ch., fixed cheeks; Jr.ch., free cheeks; g/., glabella ; ^/a./., glabellar furrows; g«., gnathobase (the free, inward projecting part of the protopodite) ; I. Jr., Hmb fringe's, for swimming and respira- tion ; l.l., lower Up or metastome; mo., mouth; pg., pygidium, covering the ab- domen ; pi., pleurae ; pr., protopodite ; u.L, upper lip or hypostome; v.m., ventral membrane. (All after Beecher, except Z).) ARTHROPODA — CRUSTACEA — TRILOBITES 287 other respects these genera are more specialized and hence less like the trilobites than Apus. Triarthrus, a trilobite crustacean, lived in the marine waters of eastern North America and northern Europe during the Ordovician period. The body was entirely incased in a chitinous skeleton, har- dened with more or less lime carbonate. Dorsally this skeleton was thickened, forming the dorsal shield; it is this which is usually preserved. It is divided into the head (or cephalon), thorax and pygidium ; two furrows extend from the front of the head to the end of the pygidium, separating a higher, narrow median portion, the axial lobe, from a lower portion on each side, the two pleural lobes. The portion of the axial lobe in the head is called the glabella ; it is large, well-defined, subquadrate and marked usually by two pairs of discontinuous furrow^s (glabellar furrows). (Com- pare gla.f. in Figs. 126 and 127.) Extending from the poste- rior angles of the head shield obliquely toward the glabella and then anteriorly to the margin is the facial suture (compare fa.s. in Figs. 126 and 128), dividing the sides of the head shield into free Sind fixed cheeks, united by uncalcified chitinous joints. The thorax is divided by transverse furrows into fourteen to sixteen segments, united by joints of chitin. The pygidium, which covers the abdomen, consists of a single piece, though the superficial grooves divide it into axial and pleural lobes. The head shield is anteriorly bent under and reflexed. To this reflected border, or doublure, was attached medially a sepa- rate plate, the upper lip, or hypostome. Posterior to this was a small convex plate, the lower lip, or metastoyne. The animal was further protected on the under side by a thin, uncalcified, chitinous membrane (Fig. 126, B) divided into an axial and two pleural portions corresponding to the axial and pleural lobes of the dorsal shield. This ventral membrane was attached to the upper and lower lips, to the reflected border of the head shield, 288 AN INTRODUCTION TO THE STUDY OF FOSSILS to the pygidium, and to the ends of the pleurae ; it was further supported by transverse, calcified, chitinous processes to which the legs were attached. Triarthrus is well called the daddy longlegs trilobite, for its appendages were unusually long for a trilobite, extending far beyond the margins of the dorsal shield. (In such forms as Trinucleus and Isotelus they did not extend to the margin of the dorsal shield.) These appendages were very uniform in char- acter from the pair directly behind the antennules to the last pair upon the abdomen. All except the most anterior pair of appendages, the anten- nules, are biramous, consisting of a basal portion : the protop- odite bearing two branches, — (i) the highly jointed endopo- dite adapted to crawling and (2) the less jointed exopodite, fringed along its posterior border by lamellae-like setae and thus adapted both to swimming and respiration. Anteriorly the endopodites are long, cylindrical, crawling legs; posteriorly they become more and more broadly flattened and leaf-like, bearing tufts of setae ; they are thus well adapted to swimming. Each protopodite has an inward projecting portion, — the jaw- like base or gnathobase. There were paired dorsal and ventral muscles beginning in the head and ending in the abdomen ; the dorsal pair extended the animal, the ventral pair flexed it ; but apparently it lacked the power of enrollment (p. 291). The ventral pair of muscles were separated by a chitinous ridge ; from each of these a muscle band extended obliquely outward and backward to the next thoracic segment to be there attached as is indicated by oblique chitinous ridges. The appendages were probably moved simi- larly to those of Apus and Cambarus. Judging from the food of the living Crustacea, Triarthrus was carnivorous, eating both decaying and living animal matter. The food brought to the ventral median line of the body by the rhythmical movement of the appendages was seized by the gna- thobases and by them carried forward to the mouth ; the broader ARTHROPOD A — CRUSTACEA — TRILOBITES 289 and stronger ones of the head may, like the mandibles of Apus, have torn the food into smaller pieces. The mouth, opening between the upper and lower lips, led into a long intestinal tube which extended backward parallel to the dorsal test, opening through the anus at the postero-ventral end of the pygidium (Fig. 126, D). The digestion of food was very likely similar to that of Apus (p. 299), except that in the absence of a stomach the digestive fluid was probably poured into the anterior portion of the intestine. Somewhat similar to the condition in Apus may likewise have been its blood circulation, excretion, its nervous system and sense organs. The intestinal tube, as well as the double chain of nerve ganglia, heart, etc., were located beneath the axial lobe in the median line of the body. Respiration took place mostly through the limb setae or fringes, aided probably by an exchange of gases through the chitinous covering of the ventral surface, which was apparently almost as thin as that covering the setae. The antennules were probably tactile organs. There is a pair of slightly raised, compound eyes situated at the inner edge of the free cheeks, while the neigh